Abstract

The electrochemical instability of Sn-based halide perovskites in aqueous media is commonly linked to surface electron accumulation and defect-assisted oxidation of Sn²⁺ to Sn⁴⁺. Here, we examine how interfacial coupling in a cesium tin chloride (CsSnCl₃)-molybdenum disulfide (MoS₂) (CSC–MS, 10%) composite electrode influences charge distribution and electrochemical behavior. Electrochemical and spectroscopic measurements indicate trends consistent with effective electronic redistribution at the interface between 𝑛-type CsSnCl₃ and 𝑝-type 2H-MoS₂, suggestive of a type-II–like alignment. Mott-Schottky analysis yields an apparent flat-band offset on the order of several hundred millivolts, which reflects an effective interfacial capacitance response rather than a uniquely defined junction potential in the heterogeneous composite electrode. Correlated trends in x-ray photoelectron spectroscopy, impedance spectroscopy, and kinetic analyses support reduced near-surface electron density in CsSnCl3 and an enhanced pseudocapacitive response. In addition, MoS₂ contributes hydrophobic basal planes and electronically active edge states that cooperatively improve interfacial stability, electronic percolation, and charge transport. As a result, the composite exhibits a kinetically extended aqueous operating window approaching 2.3 V under scan conditions and mixed charge-storage behavior in which reversible Sn²⁺/Sn⁴⁺ redox processes are contributory but not exclusive. These results provide a physically consistent, though not uniquely resolved, picture of how interfacial coupling and composite engineering can enhance the aqueous pseudocapacitive performance of lead-free halide perovskite electrodes.

Abstract

Defect engineering in orthorhombic perovskite oxides enables tunable electrochemical functionality through lattice–defect–charge coupling. Nanoporous yttrium orthoferrite (YFeO₃) synthesized via a sol-gel route exhibits controlled octahedral tilting and oxygen vacancies, enabling reversible Fe³⁺/Fe²⁺ redox transitions and extending the electrochemical stability window to 2.4 V in neutral 0.5 M Na₂SO₄ (aq). The YFeO₃ electrode delivers a specific capacitance of 216 F g⁻¹ at 1 A g⁻¹ and an energy density of 43 Wh kg⁻¹ at 1200 W kg⁻¹, retaining 91% capacitance after 10 000 galvanostatic charge–discharge cycles. Linear sweep voltammetry confirms suppression of hydrogen and oxygen evolution through defect-mediated modulation of surface electronic states. These results identify YFeO₃ as a promising high-voltage aqueous electrode. Moreover, defect–tilt coupling within the Pnma lattice emerges as a general design principle for stabilizing redox-active perovskite oxides in aqueous energy-storage systems operating at extended voltages.

Abstract

Process-induced defect-state engineering and interfacial electrostatics provide powerful routes to stabilize lead-free halide perovskites for aqueous energy-storage applications. Here, we demonstrate that defect-rich MoS₂ integrated with CsSnBr₃ forms a moisture-stable type-II n–p heterostructure that enables stable, high-voltage aqueous energy storage. The interfacial band offsets (ΔE_C ≈ −0.39 eV) generate a built-in potential of ∼0.35 V, promoting directional charge separation across the heterointerface. Vacancy-induced donor states elevate the Fermi level and reduce the activation energy by ∼0.11 eV, resulting in a 2-fold enhancement in charge-transfer rate and accelerated relaxation dynamics, as confirmed by Mott–Schottky and impedance analyses. The coupled influence of interfacial defects and the built-in electric field lowers the energy barrier for interfacial electron transfer, facilitating a defect-assisted transport pathway from CsSnBr₃ to MoS₂. Simultaneously, the hydrophobic MoS₂ overlayer electrostatically suppresses Sn²⁺ oxidation, preserving the band structure and lattice integrity during aqueous operation, as verified by XPS and FTIR. As a result, the heterostructure delivers a wide 2.8 V operating window, a high energy density of 73.9 W h kg^–1, and 90% capacitance retention after 10000 cycles. This work establishes a quantitative structure–defect–interface–performance relationship and highlights interfacially engineered perovskite heterostructures as a viable platform for moisture-stable, high-performance aqueous energy storage.

Abstract

Nanoporous orthorhombic YFeO₃ was synthesized via a citrate–ethylene glycol sol–gel auto-combustion route to elucidate how oxygen-vacancy-enabled electronic states, in conjunction with lattice distortion, govern intrinsic visible-light charge separation. Rietveld refinement confirms a phase-pure Pnma lattice with pronounced FeO₆ tilting (〈ϕ〉 ≈ 18.8 ± 0.3°) and reduced Fe–O–Fe angles, which collectively lower the oxygen-vacancy formation energy and stabilize mixed-valence Fe³⁺/Fe²⁺ centers, as supported by XPS. These defect-mediated electronic modifications, together with hierarchical mesoporosity (∼54 ± 2 nm), enhance visible-light absorption, strengthen distortion-induced internal electric fields, and facilitate directional carrier transport, thereby suppressing electron–hole recombination. Optical and photoelectrochemical analyses reveal a direct band gap of 2.34 ± 0.02 eV, n-type conductivity, an enhanced photocurrent response, and an extended carrier lifetime of 3.84 ± 0.15 ns, demonstrating that oxygen vacancies and lattice distortion act cooperatively to promote long-range charge separation. This mechanistic framework was further examined using methylene blue and levofloxacin as representative probe molecules, supporting reduced activation barriers and predominantly electron-mediated (e⁻, ˙O⁻₂) reactive oxygen species pathways. The material retained its structural and electronic integrity upon repeated operation. Overall, this work establishes a unified structure–defect–function relationship for orthorhombic YFeO₃, identifying oxygen-vacancy-enabled charge separation in a distorted lattice as a key contributor to its intrinsic visible-light functionality and providing generalizable mechanistic insights for the design of defect-engineered perovskite oxides.

Abstract

Abstract

Aqueous supercapacitors (SCs) are often constrained by low operational voltage and energy density due to the low decomposition voltage of water. In this work, we address these limitations by fabricating symmetric SCs using nanoporous dysprosium orthoferrite (DyFeO₃) electrodes in dilute, neutral aqueous electrolytes. The nanoporous architecture of the DyFeO₃ electrode material, with an average pore size of 3.41 nm, was confirmed using Brunauer–Emmett–Teller analysis and comprehensively characterized through XRD, FESEM, TEM, XPS, Raman spectroscopy, EPR, and zeta potential measurements. The fabricated SC, operating in a 0.5 M Na₂SO₄ aqueous electrolyte, exhibited a high working voltage of 2.5 V, delivering an energy density of 41.81 W h kg⁻¹ at a power density of 1250 W kg⁻¹, with 90% capacitance retention after 10 000 cycles. Furthermore, the addition of 20% acetonitrile (AN) to the 0.5 M Na₂SO₄ electrolyte extended the potential window to 3.1 V, increasing the energy density to 84.43 W h kg⁻¹ at a power density of 1550 W kg⁻¹. The fabricated symmetric SC demonstrated excellent long-term stability, retaining approximately 99% capacitance and Coulombic efficiency after a 600 hours float voltage test. These findings, for the first time, reveal the potential of nanoporous DyFeO₃ as electrode material in a 0.5 M Na₂SO₄(aq.)/20%AN electrolyte for advancing symmetric SCs, featuring an unprecedented ultra-wide electrochemical stability window along with significantly enhanced energy and power densities.

Abstract

In this study, DyFeO₃–MoS₂ heterojunction nanocomposites were synthesized by integrating porous DyFeO₃ nanoparticles (an n-type semiconductor) with MoS₂ nanosheets (a p-type semiconductor). The resulting p–n heterojunction substantially improved the photocatalytic efficiency for degrading methylene blue (MB) and levofloxacin (LFX). This design introduces a built-in electric field at the interface, promoting efficient charge separation and suppressing electron–hole recombination, thereby significantly enhancing photocatalytic performance under solar irradiation compared to DyFeO₃ alone. Characterization studies, including XRD, FESEM, TEM, XPS, UV-visible absorbance, photoluminescence, and Mott–Schottky analysis, confirmed the nanocomposites’ crystalline structure, well-dispersed MoS₂ nanosheets, oxygen vacancies, enhanced visible light absorption, and favorable band positions. The incorporation of MoS₂ increased light absorption, enhanced charge separation, and improved surface area by mitigating DyFeO₃ aggregation, leading to significantly higher photocatalytic degradation rates. Among the tested compositions, the DyFeO₃–MoS₂ (80 : 20) nanocomposite, containing 20 wt% MoS₂, exhibited the highest efficiencies, with 96.5% degradation for MB and 88.7% for LFX. Further analyses, including activation energy determination, quantum yield measurement, scavenger tests, and reusability assessments, confirmed the optimized nanocomposite's performance and durability. The reduced activation energies and high quantum yields (35.5% for MB, 25.8% for LFX) indicate efficient photon conversion and radical generation, with superoxide radicals (˙O₂⁻) identified as the primary reactive species. Stability tests revealed over 85% retention of activity after four cycles, underscoring the composite's robustness. Moreover, the photocatalytic mechanism revealed key insights into the degradation pathways of pollutants. This investigation demonstrates a viable solar-driven solution for efficient pollutant degradation in wastewater treatment by incorporating MoS₂ into porous DyFeO₃ nanostructures.

Abstract

The increasing demand for advanced materials with multifunctional magnetic properties has sparked growing interest in rare-earth and transition metal-based double perovskites. In this study, we comprehensively investigate disordered Y₂CoCrO₆ (YCCO), synthesized via the sol–gel method. Structural analysis confirms a single-phase orthorhombic crystal structure with B-site disorder, as revealed by X-ray photoelectron spectroscopy, which also identifies mixed valence states of Co and Cr due to antisite disorder and oxygen vacancies. This structural disorder profoundly impacts YCCO′s magnetic properties, leading to the emergence of a Griffiths-like phase, detected through inverse susceptibility measurements. Additionally, the material exhibits both antiferromagnetic and weak ferromagnetic behaviors, evidenced by a negative Curie–Weiss temperature and unsaturated magnetic hysteresis loops. Arrott plot analysis indicates a second-order phase transition and magnetocaloric measurements reveal a maximum entropy change (S_max) of 0.217 J kg⁻¹ K⁻¹, a relative cooling power (RCP) of 17.36 J kg⁻¹, and a temperature averaged entropy change (TEC) of 0.17 J kg⁻¹ K⁻¹ over a temperature span (T_lift) of 30 K under a 5 T field, showcasing its potential for low-temperature and multistage cooling applications. Although its modest magnetocaloric effect (MCE) performance is attributed to its antiferromagnetic nature with weak ferromagnetic contributions and a low Curie temperature, this work represents a significant step in unveiling the potential of YCCO for multifunctional applications. Future optimization through chemical doping, nanostructuring, and compositional modifications is proposed to enhance its magnetocaloric and functional properties, positioning YCCO as a strong candidate for advanced magnetic and cooling technologies.

Abstract

In this study, we present a comprehensive theoretical and experimental investigation into the electronic structure, optical properties, and photocatalytic potential of Gd₂CoCrO₆ (GCCO) double perovskite. Using first-principles calculations with the generalized-gradient-approximation plus Hubbard U (GGA + U) method, we explored the effects of Coulomb interactions on the electronic properties. Our calculations revealed that GCCO exhibits a half-metallic nature, displaying metallic behavior for up-spin and semiconducting behavior for down-spin states. The optimized U_eff value of 4.2 eV accurately reproduces the direct bandgap of 2.25 eV, which aligns closely with experimental results obtained through UV-visible absorption spectroscopy and photoluminescence analysis. Additionally, time-resolved photoluminescence (TRPL) measurements indicate a mean charge carrier lifetime of 2.37 ns, suggesting effective charge separation. Mott–Schottky analysis and valence band X-ray photoelectron spectroscopy (XPS) confirm the n-type semiconducting nature of GCCO with favorable band edge positions for redox reactions. The combination of theoretical insights and experimental characterization indicates that GCCO holds significant promise as a photocatalyst for applications in renewable energy production and environmental remediation, particularly in solar-driven water splitting and pollutant degradation. Our study provides crucial insights into the electronic structure and optical properties of double perovskites like GCCO, highlighting their suitability for photocatalytic applications. Furthermore, the research paves the way for future work in the compositional engineering and defect modulation of double perovskites to optimize their photocatalytic efficiency.

Abstract

Pharmaceutical wastewater contamination, particularly from antibiotics, poses severe environmental and health risks due to antibiotic-resistant bacteria and the inefficacy of conventional treatments. In this study, BiFe_0.5Cr_0.5O₃ (BFCO) nanoparticles were synthesized via the sol–gel method and investigated as a visible-light-driven photocatalyst for ciprofloxacin (CIP) and levofloxacin (LFX) degradation under solar irradiation. The structural analysis confirmed a single-phase perovskite structure with Cr³⁺ incorporation, enhancing charge separation and visible-light absorption. The presence of oxygen vacancies, identified through XPS and Raman spectroscopy, played a crucial role in charge transfer and reactive oxygen species (ROS) generation. Comprehensive electrochemical and photoelectrochemical analyses, including CV, LSV, and EIS, confirmed enhanced charge transport and reduced interfacial resistance under illumination. BFCO, with a bandgap of 1.87 eV, exhibited efficient solar energy utilization, achieving 70.35% CIP and 94% LFX degradation within 240 minutes, following pseudo-first-order kinetics. The activation energy decreased from 33.61 ± 5.88 to 19.69 ± 3.94 kJ mol⁻¹ K⁻¹, confirming enhanced catalytic efficiency. An apparent quantum yield (AQY) of 34.9% for LFX further underscored its superior activity. Scavenger studies identified electron (e⁻) and superoxide (˙O₂⁻) radicals as key ROS driving antibiotic degradation, while oxygen vacancies improved charge separation and ROS formation. Reusability tests confirmed BFCO's stability across multiple cycles, maintaining its structural, morphological, and optical integrity. The degradation mechanism involves solar-induced electron–hole pair generation, charge transfer to oxygen vacancies, and subsequent redox reactions that break down antibiotics into non-toxic byproducts. The synergistic effects of Cr substitution, oxygen vacancies, and mixed-valence states significantly enhanced photocatalytic efficiency, demonstrating BFCO's potential for large-scale environmental remediation.

Abstract

In this investigation, nanoparticles of B-site disordered Y₂NiCrO₆ (YNCO) double perovskite were synthesized by the facile sol–gel method to evaluate their magnetic and electrochemical properties. Their crystallographic structure is monoclinic and the average size of the particles is 79 ± 16 nm. XPS analysis indicated a mixed oxidation states of B-site transition metals Ni²⁺/Ni³⁺ and Cr²⁺/Cr³⁺. The mixed valence states of Ni and Cr, along with the mixed magnetic phases of YNCO, constitute a signature of the B-site disorder. This antisite disorder contributed to the observation of a Griffiths-like phase arising from ferromagnetic short-range interactions above the magnetic transition up to the Griffiths temperature, T_G = 137 K. The synthesized YNCO double perovskite demonstrated a promising behavior as an electrode material for electrochemical supercapacitors. In a three-electrode system, it displayed a specific capacitance of 270 F g⁻¹ at a current density of 0.5 A g⁻¹. In a symmetric two-electrode system, YNCO exhibited a specific capacitance of 180 F g⁻¹ at 0.5 A g⁻¹, alongside an energy density of 6.25 Wh kg⁻¹ at 250 W kg⁻¹ power density. In both cases, we employed a mild 0.5 M neutral aqueous Na₂SO₄ solution as the electrolyte, in contrast to the typically employed corrosive and concentrated alkaline aqueous solution. The fascinating magnetic and charge storage properties of the B-site disordered YNCO double perovskite indicate its potential for use in spintronic devices and as efficient electrodes in symmetric hybrid supercapacitors.

Abstract

In this investigation, moisture-stable CsSnBr₂Cl nanoparticles were synthesized by incorporating Cl into CsSnBr₃ halide perovskite using the hot injection method. Various analyses including XRD, XPS, UV–vis absorbance, photoluminescence, and Mott–Schottky have confirmed that the structural properties, chemical states, optical properties, and electronic band structure of CsSnBr₂Cl nanoparticles remain intact even after 75 days of water immersion, thereby conclusively demonstrating their moisture stability. In a three-electrode system, the comparative electrochemical performance of pristine CsSnBr₃ nanoparticles and moisture-stable Cl-incorporated CsSnBr₂Cl nanoparticles was evaluated in various aqueous electrolytes, including HCl, Na₂SO₄, and KOH. The results indicate that the CsSnBr₂Cl electrode material exhibits superior electrochemical properties, such as a larger integrated cyclic voltammetry (CV) area, a wider potential window, longer charge–discharge times, and lower impedance parameters compared to the pristine CsSnBr₃ nanoparticles. The electrochemical performance of CsSnBr₂Cl nanoparticles was evaluated for potential applications in batteries, supercapacitors, fuel cells, and water splitting, with a focus on reaction kinetics, charge storage mechanisms, and impedance parameters. The electrochemical properties of the nanoparticles were assessed using a three-electrode configuration across various 0.5 M aqueous electrolytes (HCl, Na₂SO₄, and KOH). In HCl, the nanoparticles demonstrated impressive charge storage capability, achieving a capacitance of 474 F g^–1 at 1 A g^–1, affirming their suitability for energy storage devices. In Na₂SO₄(aq.), the nanoparticles exhibited excellent stability for supercapacitors, operating up to 1.6 V without significant oxygen evolution. Notably, in KOH, they demonstrated potential as effective water-splitting electrodes. The practical applicability of the nanoparticles was evaluated using a symmetric two-electrode configuration with HCl and Na₂SO₄ electrolytes. The capacitance values were 117 F g^–1 in HCl and 70 F g^–1 in Na₂SO₄ at 1 A g^–1. Notably, after 5000 GCD cycles in HCl(aq.), the nanoparticles retained 93% of their capacitance and maintained 91% Coulombic efficiency. They also demonstrated stable operation across a temperature range of 3 to 60 °C, achieving an energy density of 5.83 W h kg^–1 at a power density of 600 W kg^–1. This study emphasizes the considerable potential of CsSnBr₂Cl nanoparticles in advancing electrochemical energy storage technologies and sets a solid foundation for future research and development in metal halide perovskites.

Abstract

The persistent issue of water contamination by industrial dyes and pharmaceutical residues has created an urgent need for advanced photocatalytic materials to effectively address environmental remediation. Despite ongoing research, developing novel photocatalysts with ideal band structures, high quantum yields, and strong stability remains a considerable challenge. In this study, we report the synthesis and detailed characterization of nanostructured dysprosium orthoferrite (DyFeO₃) nanoparticles, designed with a porous architecture featuring an average pore size of 3.41 nm and a surface area of 23.25 m² g⁻¹ to enhance photocatalytic efficiency under solar irradiation. Using Inverse Fast Fourier Transform (FFT) analysis on selected areas of TEM images, we gained deeper insights into the formation and internal structure of these nanoparticles. DyFeO₃ nanoparticles exhibit a direct band gap of 2.1 eV, making them particularly effective for solar light absorption. Comprehensive spectroscopic analyses, including Mott–Schottky measurements and valence band XPS, confirmed their n-type semiconducting nature and revealed an electronic band structure that supports efficient oxygen reduction and oxidation reactions. Additionally, time-resolved photoluminescence spectroscopy demonstrated a charge carrier lifetime of 2.43 ns, indicating efficient separation and transport of photogenerated charge carriers. The photocatalytic performance of DyFeO₃ was evaluated through degradation experiments using two model pollutants: Rhodamine B (RhB) and Levofloxacin (LFX). The nanoparticles successfully degraded both the colored RhB and the colorless LFX, eliminating concerns of dye sensitization. Furthermore, the presence of DyFeO₃ significantly reduced the activation energy for RhB degradation from 55.87 kJ mol⁻¹ K⁻¹ to 34.58 kJ mol⁻¹ K⁻¹ and for LFX from 38.4 kJ mol⁻¹ K⁻¹ to 34.1 kJ mol⁻¹ K⁻¹, demonstrating its catalytic efficiency. With apparent quantum yield values of 28.94% for RhB and 32.83% for LFX, these nanoparticles demonstrate exceptional solar energy harvesting capabilities. The high degradation efficiency, quantum yield, and stability of the single-structured DyFeO₃ nanoparticles highlight their potential for large-scale applications in photocatalytic and environmental remediation technologies.

Abstract

A facile sol-gel synthesis method was employed to synthesize dysprosium chromite (DyCrO₃) nanoparticles (NPs), which were subsequently calcined at 750 ^∘C to investigate their structural, optical, and photocatalytic properties. Rietveld refinement of powder X-ray diffraction patterns revealed a single-phase orthorhombic structure for the DyCrO₃ NPs, exhibiting good crystallinity and belonging to the Pbnm space group. Furthermore, Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy imaging revealed a promising morphology with an average particle size of 30 ± 7 nm. Optical assessments indicated an energy band gap of 2.72 eV, suggesting potential for solar light harvesting as a photocatalyst. Mott-Schottky plots confirmed the n-type semiconductor behavior of the DyCrO₃ NPs, and valence band X-ray photoelectron spectroscopy analysis supported these findings. Electronic band structure calculations showed a substantial conduction band minimum and a positive valence band maximum, essential for promoting oxygen reduction and oxidation reactions, respectively, which are crucial for photocatalytic activity. Moreover, the synthesized DyCrO₃ NPs demonstrated significant potential as efficient photocatalysts, effectively decomposing the antibiotic ciprofloxacin (CIP) under solar light. Notably, the DyCrO₃ NPs achieved 83 % degradation of CIP within 240 min of solar irradiation. Similarly, under identical conditions, the DyCrO₃ NPs photocatalyst showed promise in degrading 70 % of the colored organic pollutant methylene blue (MB). Interestingly, during the first 120 min, the degradation of CIP was approximately 25 % greater than that of MB. The ability of DyCrO₃ NPs to efficiently degrade both colored and colorless pollutants highlights the catalyst’s inherent photocatalytic nature, rather than merely relying on dye-sensitization effects. Furthermore, the presence of DyCrO₃ NPs reduced the activation energy for CIP degradation from 31.657 kJ mol⁻¹ K⁻¹ to 20.846 kJ mol⁻¹ K⁻¹, providing additional evidence of their true catalytic efficacy. Apparent quantum yield values of 40 % for CIP and 35 % for MB degradation further illustrate their superior solar energy harvesting ability. A comprehensive mechanism was developed to explain the impressive photocatalytic performance of the synthesized NPs, highlighting their potential in degrading pharmaceutical antibiotics.

Abstract

We explored a comprehensive comparison of the structure–property relationships between sillenite and perovskite phases of Bi_0.9Dy_0.1FeO₃ (BDFO) nanostructures synthesized by hydrothermal (HT) and sol–gel (SG) techniques. The role of sillenite/perovskite phases as well as oxygen vacancies in the magnetic and catalytic properties was analyzed and compared, which to our knowledge, is the first of its kind at the nanometer scale. XRD results revealed the formation of a sillenite dominating phase through the HT synthesis at 160 °C, whereas, the SG method resulted in perovskite bismuth ferrite after calcination at an elevated temperature of 600 °C. Both scanning and transmission electron microscopy imaging demonstrated a mixed nanopowder and rod-like morphology of the materials synthesized by the HT technique, however, semi-spherical particles with a particle size of B100 nm were produced via the SG technique. The XPS analysis revealed that the number of oxygen vacancies was higher in the HT-synthesized BDFO compared to that of the SG-synthesized BDFO. A sharp transition of the HT-synthesized BDFO materials was observed at 43 K, whereas, the SG-synthesized materials revealed a gradual increase in the magnetization with the decrement of temperature from 400 to 5 K without any phase transition. The HT-synthesized BDFO demonstrated a better photocatalytic performance to degrade rhodamine B and colorless antibiotic ciprofloxacin compared to the SG-synthesized BDFO photocatalyst. This comprehensive analysis of the phase-structure, morphology, chemical states, and oxygen vacancies of BDFO materials synthesized under the standard synthesis conditions of two commonly used synthesis techniques might be helpful for researchers to understand the physico-chemical properties of analogous nanostructures for desired applications.

Abstract

In this present investigation, nanoparticles of B-site disordered Y₂FeCrO₆ (YFCO) double perovskite have been successfully synthesized for the first time by optimizing synthesis steps and temperatures of facile sol-gel technique to investigate their structural, magnetic, and optical properties. The Rietveld refinement of the X-ray diffraction pattern of YFCO nanoparticles revealed a single-phase orthorhombic structure with pbnm space group. The average size of the nanoparticles is around 67 ± 15 nm determined by both field emission scanning electron microscopy and transmission electron microscopy imaging. The existence of mixed valence states of Fe and Cr ions was confirmed by X-ray photoelectron spectroscopy which is an indication of the absence of proper B site long range ordering. The temperature dependent magnetization curves demonstrated negative magnetization of this double perovskite material with compensation temperature at around 170 K. The field-dependent magnetic hysteresis loops exhibited the coexistence of weak ferromagnetic and antiferromagnetic domains in YFCO nanoparticles. The exchange bias effect was observed below Néel temperature which is tunable by a cooling magnetic field. The UV–visible spectroscopy ensured that YFCO nanoparticles have a direct band gap of ∼ 1.90 eV, which was further confirmed by steady-state photoluminescence spectroscopy. This B-site disordered YFCO might enhance interest on basic fundamental research on disordered rare-earth and transition metal-based perovskite systems and can be used for spintronics as well as photocatalytic applications because of its favorable magnetic and optical properties.

Abstract

We have synthesized disordered double perovskite Gd₂CoCrO₆ (GCCO) nanoparticles with an average particle size of 71 ± 3 nm by adopting a citrate sol–gel method to investigate their structural, magnetic, and optical properties. Rietveld refinement of the X-ray diffraction pattern showed that GCCO is crystallized in a monoclinic structure with space group P21/n, which is further confirmed by Raman spectroscopic analysis. The absence of perfect long-range ordering between Co and Cr ions is confirmed by the mixed valence states of Co and Cr. A Neel transition was observed at a higher ´ temperature of T_N = 105 K compared to that of an analogous double perovskite Gd₂FeCrO₆ due to a greater degree of magnetocrystalline anisotropy of Co than Fe. Magnetization reversal (MR) behavior with a compensation temperature of T_comp = 30 K was also observed. The hysteresis loop obtained at 5 K exhibited the presence of both ferromagnetic (FM) and antiferromagnetic (AFM) domains. Superexchange and Dzyaloshinskii–Moriya (DM) interactions between various cations via oxygen ligands are responsible for the observed FM or AFM ordering in the system. Furthermore, UV-visible and photoluminescence spectroscopy demonstrated the semiconducting nature of GCCO with a direct optical bandgap of 2.25 eV. The Mulliken electronegativity approach revealed the potential applicability of GCCO nanoparticles in photocatalytic H₂ and O₂ evolution from water. Due to a favorable bandgap and potentiality as a photocatalyst, GCCO can be a promising new member of double perovskite materials for photocatalytic and related solar energy applications. 

Abstract

In this investigation, molybdenum disulfide (MoS₂) nanosheets, copper cobalt sulfide (CuCo₂S₄) nanomaterials, and MoS₂ incorporated CuCo₂S₄–MoS₂ nanocomposites were synthesized as electrode materials for hybrid supercapacitors. The concentrations of MoS2 were varied and optimized for the synthesis of CuCo₂S₄–MoS₂ nanocomposites to improve their electrochemical properties for use in high-performance energy storage devices. The successful formation of CuCo₂S₄–MoS₂ nanocomposites was confirmed by powder XRD analysis, TEM imaging and X-ray photoelectron spectroscopy analyses. In a three-electrode system, compared to other synthesized electrode materials, the CuCo₂S₄–MoS₂ (80 : 20) nanocomposite with a 20 wt% concentration of MoS₂ demonstrated the highest specific capacitance of 1333 F g1 at 1 A g1 current density and 94% capacitance retention after 5000 charge–discharge cycles. Notably, in a symmetric two-electrode configuration, the optimized CuCo₂S₄–MoS₂ (80 : 20) nanocomposite also exhibited the highest specific capacitance of 670 F g1 at 1 A g1 current density and achieved an energy density of 33.5 W h kg1 at 600 W kg1 power density compared to that of other synthesized electrode materials. Finally, a prototype supercapacitor was assembled by utilizing the optimized CuCo₂S₄–MoS₂ (80 : 20) nanocomposite as an electrode material via a coin cell to light up an LED. Our findings demonstrate that incorporation of MoS₂ improves electrochemical performance and 20 wt% MoS₂ is the optimum concentration to significantly enhance the charge storage capacity, conductivity, and stability of CuCo₂S₄. The charge storage mechanism of the optimized nanocomposite in a symmetric two-electrode system was comprehensively discussed. The outcome of this investigation demonstrated that the optimized CuCo₂S₄–MoS₂ (80 : 20) nanocomposite with its high charge storage capacity, energy density, and excellent long-term stability can be used as an efficient electrode material for high-performance symmetric hybrid supercapacitors.

Abstract

In this investigation, we have demonstrated the synthesis of lead-free CsSnBr₃ (CSB) and 5 mol% bismuth (Bi) doped CSB (CSB′ B) nanocrystals, with a stable cubic perovskite structure following a facile hot injection technique. The Bi substitution in CSB was found to play a vital role in reducing the size of the nanocrystals significantly, from 316 ± 93 to 87 ± 22 nm. Additionally, Bi doping has inhibited the oxidation of Sn²⁺ of CSB perovskite. A reduction in the optical band gap from 1.89 to 1.73 eV was observed for CSB′ B and the PL intensity was quenched due to the introduction of the Bi³⁺ dopant. To demonstrate one of the visiblelight-driven applications of the nanocrystals, photodegradation experiments were carried out as a test case. Interestingly, under UV-vis irradiation, the degradation efficiency of CSB′ B was roughly one order lower than that of P25 titania nanoparticles; however, it was almost five times higher when driven by visible light under identical conditions. The water stability of CSB′ B perovskite and suppression of the oxidative degradation of Sn were confirmed through XRD and XPS analyses after photocatalysis. Moreover, by employing experimental parameters, DFT-based first-principles calculations were performed, which demonstrated an excellent qualitative agreement between experimental and theoretical outcomes. The assynthesized Bi-doped CSB might be a stable halide perovskite with potential in visible-light-driven applications

Abstract

In this investigation, BiFeO₃ (BFO) and 10% La-doped BiFeO₃ (BLFO) nanoceramics were synthesized by a sol–gel method for the photocatalytic degradation of colorless antibiotics ciprofloxacin and levofloxacin under the irradiation of 500 W Hg-Xe lamp. A good agreement between the structural transitions from rhombohedral to orthorhombic phase was observed by the X-ray diffraction and the vibrational modes in the Raman spectra, due to the substitution of Bi by La. Moreover, La doping resulted in a decrease in the particle size from ∼117 to 32 nm, reduction of oxygen vacancies, significant enhancement of magnetization, dramatic improvement of optical absorption, and reduction of band gap from 2.19 to 2.14 eV. The significantly enhanced magnetization might be associated with the suppression of the spiral spin cycloid of BFO due to the substitution of La and reduced size of the BLFO nanoceramics to ∼32 nm which was also confirmed by transmission electron microscopy imaging. The strong optical absorption of BLFO nanoceramics boosted their photo-generated charge carriers separation, produced more reactive species, and demonstrated ∼70% photocatalytic efficiency to degrade pharmaceutical pollutants from aqueous solution. The high saturation magnetization and strong optical absorption mostly in the visible region suggest the potentiality of BLFO nanoceramics as a promising photocatalyst with a superior recyclability to be magnetically extracted from the reaction medium.

Abstract

Dysprosium chromite (DyCrO₃) nanoparticles and dysprosium chromite-reduced graphene oxide (DyCrO₃-rGO) nanocomposite were synthesized by using a hydrothermal technique. The rGO incorporated DyCrO₃-rGO photocatalyst demonstrated up to 87% efficiency to degrade rhodamine B dye which is higher than those of DyCrO₃ and commercial Degussa P25 titania nanoparticles. DyCrO₃-rGO also generated approximately 3 times greater amounts of hydrogen via water splitting compared to that produced by the P25 titania nanoparticles. The outcome of this investigation might be helpful for synthesizing rGO-based nanocomposite heterostructures for superior solar energy-driven applications.

Abstract

Ternary transition metal sulfides have emerged as promising electrode materials for next-generation supercapacitors because of their potential ability to simultaneously ensure high conductivity and stability during electrochemical reactions. In the present investigation, MoS₂ incorporated CuCo₂S₄ nanocomposites have been successfully synthesized using a hydrothermal technique. The structural, morphological, elemental and chemical properties of the prepared CuCo₂S₄–MoS₂ nanocomposite were investigated extensively. High resolution transmission electron microscopy imaging demonstrated the successful synthesis of CuCo₂S₄–MoS₂ nanocomposites. The electrochemical capacitor performance of the nanocomposite has been evaluated both in three-electrode and symmetric two-electrode systems. In the three-electrode cell, a specific capacitance of 820 F g⁻¹ was achieved for the CuCo₂S₄–MoS₂ electrode at a current density of 0.5 A g⁻¹ which is considerably higher than that of the CuCo₂S₄ electrode (249 F g⁻¹). We observed that the charge storage capacity, conductivity and stability of CuCo₂S₄ improved significantly due to the incorporation of MoS₂. Finally, an asymmetric supercapacitor was fabricated by assembling the CuCo₂S₄–MoS₂ electrode with an activated carbon electrode which demonstrated a large stable working potential window of 1.6 V. Excellent long-term cyclic stability of 89% retention after 1000 galvanostatic charge-discharge cycles was evident. As a solid state device, it delivered a high energy density of 38.22 W h kg⁻¹ at a power density of 400 W kg⁻¹ and lit up one red LED for 170 s, indicating its superiority over the conventional Cu-Co based supercapacitors.

Abstract

Here, we report on the structural, vibrational phonon, electrical, and magnetic properties of undoped strontium titanate SrTiO₃, Ce doped Sr_1−xCe_xTiO₃, and (Ce, Fe) co-doped Sr_1−xCe_xTi_1−yFe_yO₃ samples synthesized through solid state reaction route. The Rietveld refined powder x-ray diffraction analysis confirmed the cubic Pm-3m phase in our as-synthesized samples. We observed grain size reduction in SrTiO₃ from scanning electron micrographs due to the incorporation of Ce and Fe dopants. The sample purity in terms of chemical species identification has been confirmed from energy-dispersive x-ray spectroscopy. The characteristic phonon modes in our samples are identified using room temperature Raman spectroscopy and benchmarked against existing relevant experimental observations. The incorporation of Ce and Fe as substitutional dopants in SrTiO₃ unit cell was confirmed from the absence of absorption at 480, 555, 580, and 1635 cm⁻¹ band in Fourier transform infrared spectra. The 3% Ce doping in Sr_0.97Ce_0.03TiO₃ sample may have induced ferroelectric order, whereas the undoped SrTiO₃ (STO) revealed lossy paraelectric nature. In the case of (Ce = 3%, Fe = 10%) co-doped Sr_0.97Ce_0.03Ti_0.90Fe_0.10O₃ sample, we observed ferromagnetic hysteresis with orders of magnitude enhancement in remnant magnetization and coercivity as compared to undoped STO sample. This long range robust ferromagnetic order may have originated from F-center mediated magnetic interaction.

Abstract

Sillenite-type members of the bismuth ferrite family have demonstrated outstanding potential as novel photocatalysts in environmental remediation such as organic pollutant degradation. This investigation has developed a low temperature one-step hydrothermal technique to fabricate sillenite bismuth ferrite Bi₂₅FeO₄₀ (S-BFO) via co-substitution of 10% Gd and 10% Cr in Bi and Fe sites of BiFeO₃, respectively, by tuning hydrothermal reaction temperatures. Rietveld refined X-ray diffraction patterns of the as-synthesized powder materials revealed the formation of S-BFO at a reaction temperature of 120–160 °C. A further increase in the reaction temperature destroyed the desired sillenite structure. With the increase in the reaction temperature from 120 to 160 °C, the morphology of S-BFO gradually changed from irregular shape to spherical powder nanomaterials. The high-resolution TEM imaging demonstrated the polycrystalline nature of the S-BFO(160) nanopowders synthesized at 160 °C. The as-synthesized samples exhibited considerably high absorbance in the visible region of the solar spectrum, with the lowest band gap of 1.76 eV for the sample S-BFO(160). Interestingly, S-BFO(160) exhibited the highest photocatalytic performance under solar irradiation, toward the degradation of rhodamine B and methylene blue dyes owing to homogeneous phase distribution, regular powder-like morphology, lowest band gap, and quenching of electron–hole pair recombination. The photodegradation of a colorless organic pollutant (ciprofloxacin) was also examined to ensure that the degradation is photocatalytic and not dye-sensitized. In summary, Gd and Cr co-doping have proven to be a compelling energy-saving and low-cost approach for the formulation of sillenite-phase bismuth ferrite with promising photocatalytic activity.

Abstract

The development of metal oxide photocatalysts with improved dye degradation efficiency under natural sunlight is in increasing demand due to their superior chemical stability and cost effectiveness. In this context, Gd and Y co-doped BiVO₄ having the nominal compositions Bi_0.92Gd_xY_yVO₄(0.06 ≤ x ≤ 0.08; 0 ≤ y ≤ 0.02) have been synthesized via a surfactant free hydrothermal technique. The structural characterizations by X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy confirmed a monoclinic to tetragonal phase transition induced by co-doping in BiVO₄. High resolution transmission electron microscopy images revealed successful synthesis of Gd and Y co-doped BiVO₄ with a very good crystallinity. The steady-state photoluminescence spectroscopy analysis indicated significant suppression of charge carrier recombination in the co-doped samples. Under simulated sunlight, Bi_0.92Gd_0.07Y_0.01VO₄ photocatalyst demonstrated 94% degradation of methylene blue dye (MB) within 90 min of irradiation time, which is about 4 times higher than that of pristine BiVO₄ photocatalyst. This superior photocatalytic performance may be attributed to the synergistic effect of nanorod like shape of the synthesized materials, negative surface charge, and enhanced charge career lifetime of the Bi_0.92Gd_0.07Y_0.01VO₄ photocatalyst.

Abstract

Here, the first-principles predictions on the structural stability, magnetic behavior and electronic structure of B-site ordered double perovskite Nd₂CrFeO₆ have been reported. Initially, the ground state of the parent single perovskites NdCrO₃ and NdFeO₃ have been studied to determine the relevant U value to investigate the properties of Nd₂CrFeO₆. The thermodynamic, mechanical, and dynamic stability analyses suggest the possibility of the synthesis of Nd₂CrFeO₆ double perovskite at ambient pressure. The compound shows ferrimagnetic (FiM) nature with 2 μ_B net magnetic moment and the magnetic ordering temperature has been estimated to be ~265 K. Electronic structure indicates higher probability of direct photon transition over the indirect transition with a band gap of ~1.85 eV. Additional effect of Nd (4f) spin and spin-orbit coupling (SOC) on the band edges have been found to be negligible for this 4f-3d-3d spin system. This first-principles investigation predicts that due to the FiM nature and significantly lower band gap compared to its antiferromagnetic (AFM) parent single perovskites, B-site ordered Nd₂CrFeO₆ double perovskite could be a promising material for sprintonic and visible-light driven energy device applications.

Abstract

This investigation highlights the synthesis of an efficient photocatalyst, 10% gadolinium (Gd) doped BiFeO₃ (BGFO), via a facile hydrothermal technique at a lower reaction temperature of 160 ^∘C and its effective application towards the degradation of industrial effluents, such as rhodamine B (RhB), methylene blue (MB) and pharmaceutical pollutants such as ciprofloxacin (CIP), levofloxacin (LFX) under solar irradiation. The successful fabrication of the photocatalyst was confirmed by the Rietveld refined powder X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses. The high-resolution transmission electron microscope imaging demonstrated the formation of nanoparticles with excellent morphology and very good crystallinity. The optical characterizations revealed a reduction in the optical bandgap from 1.95 to 1.18 eV, as well as effective suppression of electron-hole pair recombination in the BGFO sample. Notably, the photocatalyst BGFO demonstrated 96% and 97% degradation of RhB and MB within 240 and 180 min of solar irradiation, respectively. Moreover, the photodegradation of colorless organic contaminants CIP and LFX was also examined to evaluate the photosensitization properties. Interestingly, about 80% and 79% degradation of CIP and LFX was obtained within 240 min of solar irradiation. The enhanced photocatalytic activities of BGFO could be attributed to the excellent morphology, good crystallinity, increased optical absorption, and effective separation of the photogenerated charge carriers. Additionally, based on the band structures, a plausible mechanism was proposed to comprehend the rationale behind the influential photocatalytic performance of the synthesized nanoparticles to explore their potential towards the future of wastewater treatment on an industrial scale.

Abstract

Lead-free double perovskites are overtaking single perovskites as solar harvesting materials due to their superior stability, excellent catalytic efficiency and minimal toxicity. In this investigation, we have synthesized double perovskite Gd₂FeCrO₆ (GFCO) nanoparticles for the first time via a facile sol-gel technique to investigate their structural, magnetic and optical properties. The double perovskite GFCO crystallized in monoclinic structure with P2₁/n space group. The Fe/Cr-O bond length was calculated as ~ 1.95 Å from the Raman spectrum which was consistent with the value, ~ 1.99 Å obtained from X-ray diffraction analysis. The average size of the nanoparticles was determined to be ~ 70 nm by both field emission scanning electron microscopy and transmission electron microscopy. The existence of mixed valence states of Fe and Cr was confirmed by X-ray photoelectron spectroscopy. The zero field cooled (ZFC) and field cooled (FC) curves largely diverged below 20 K. A downturn was observed in the ZFC curve at 15 K which corresponds to an antiferromagnetic, Néel transition. The narrow magnetic hysteresis loop recorded at 5 K was nearly saturated and demonstrated an asymmetric shift along the magnetic field axis indicating the concurrence of ferromagnetic and antiferromagnetic domains in GFCO nanoparticles. The UV–visible and photoluminescence spectroscopic analyses unveiled the semiconducting nature of nanostructured GFCO with an optical band gap of 2.0 eV. The as-synthesized thermally stable lead-free GFCO semiconductor might be a potential perovskite material to be employed in photocatalytic and related solar energy applications due to its ability to absorb the visible spectrum of the solar light.

Abstract

Fabrication of heterogeneous photocatalysts has received increasing research interest due to their potential applications for the degradation of organic pollutants in wastewater and evolution of carbon-free hydrogen fuel via water splitting. Here, we report the photodegradation and photocatalytic hydrogen generation abilities of nanostructured LaFeO₃-MoS₂ photocatalyst synthesized by facile hydrothermal technique. Prior to conducting photocatalytic experiments, structural, morphological and optical properties of the nanocomposite were extensively investigated using X-ray diffraction analysis, field emission scanning electron microscopy and UV-visible spectroscopy, respectively. Nanostructured LaFeO₃-MoS₂ photodegraded ~96% of rhodamine B dye within only 150 minutes which is considerably higher than that of LaFeO₃ and commercial Degussa P25 titania nanoparticles. The LaFeO₃-MoS₂ nanocomposite also exhibited significantly enhanced photocatalytic efficiency in the decomposition of a colorless probe pollutant, ciprofloxacin eliminating the possibility of the dye-sensitization effect. Moreover, LaFeO₃-MoS₂ demonstrated superior photocatalytic activity towards solar hydrogen evolution via water splitting. Considering the band structures and contribution of reactive species, a direct Z-scheme photocatalytic mechanism is proposed to rationalize the superior photocatalytic behavior of LaFeO₃-MoS₂ nanocomposite.

Abstract

We have synthesized Gd₂FeCrO₆ (GFCO) double perovskite which crystallized in monoclinic structure with P2₁/n space group. The UV-visible and photoluminescence spectroscopic analyses confirmed its direct band gap semiconducting nature. Here, by employing experimentally obtained structural parameters in first-principles calculation, we have reported the spin-polarized electronic band structure, charge carrier effective masses, density of states, electronic charge density distribution and optical absorption property of this newly synthesized GFCO double perovskite. Moreover, the effects of on-site d-d Coulomb interaction energy (U_eff) on the electronic and optical properties were investigated by applying a range of Hubbard U_eff parameter from 0 to 6 eV to the Fe-3d and Cr-3d orbitals within the generalized gradient approximation (GGA) and GGA+U methods. Notably, when we applied U_eff in the range of 1 to 5 eV, both the up-spin and down-spin band structures were observed to be direct. The charge carrier effective masses were also found to enhance gradually from U_eff = 1 eV to 5 eV, however, these values were anomalous for U_eff = 0 and 6 eV. These results suggest that U_eff should be limited within the range of 1 to 5 eV to calculate the structural, electronic and optical properties of GFCO double perovskite. Finally we observed that considering U_eff = 3 eV, the theoretically calculated optical band gap ∼1.99 eV matched well with the experimentally obtained value ∼2.0 eV. The outcomes of our finding imply that the U_eff value of 3 eV most accurately localized the Fe-3d and Cr-3d orbitals of GFCO keeping the effect of self-interaction error from the other orbitals almost negligible. Therefore, we may recommend U_eff = 3 eV for first-principles calculation of the electronic and optical properties of GFCO double perovskite that might have potential in photocatalytic and related solar energy applications.

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In this article, we report the structural, dielectric, electronic, and transport properties of Mo and W doped BaTiO₃ ceramic. The BaTiO₃ (BTO), BaTi_0.85Mo_0.15O₃ (BTMO), and BaTi_0.85W_0.15O₃ (BTWO) samples were prepared by double sintering ceramic technique. The  X-ray diffraction patterns confirmed the tetragonal phase of the perovskite structure with the P4mm space group including some extra phases in BTMO and BTWO. A relaxation peak in the real part of electric modulus (M’’)is observed for BTO and BTMO at  3kHz. The dielectric constants, (ε_{r^{' ,}} ε_r^'') and loss tangent (tanδ) for all samples were measured from 300 K to 450 K under the application of 100kHz electric field and temperature dependent dielectric anomalies ensure a ferroelectric (tetragonal) to paraelectric (cubic) phase transition in all samples. BTO and BTMO crystals display between normal ferroelectric and ideal relaxor behavior while BTWO crystal approaches to ideal relaxor ferroelectric behavior identified as canonical relaxor. Moreover, solid–liquid state anisotropy during the phase transition in all samples has been illustrated in terms of Fr ̈ohlich entropy. Apart from this, in BTO and BTWO samples, the conduction mechanism is highly dominated by the frequency of applied field compared to BTMO sample. Moreover, all studied samples exhibit semiconducting behavior with positive temperature coefficient of resistance (PTCR) effect in between 300 K and 450 K. The BTMO sample with maximum PTCR peak (2.9%/K at 415K) may find suitability for temperature controlled device application. 

Abstract

Photocatalytic water splitting has greatly stimulated as an ideal technique for producing hydrogen (H₂) fuel by employing two renewable sources, i.e., water and solar energy. Here, we have adopted a facile hydrothermal approach for the successful synthesis of reduced graphene oxide (rGO) incorporated Fe/MgO nanocomposites followed by thermal treatment at inert atmosphere to investigate their ability for photodegradation and photocatalytic hydrogen evolution via water splitting. Transmission Electron Microscopy images of Fe/ MgO-rGO nanocomposite ensured the distribution of Fe/MgO nanoparticles throughout rGO sheets. Notably, all rGO supported nanocomposites, especially the one, thermally treated at 500 ^oC at Argon (Ar) atmosphere has demonstrated significantly higher photocatalytic efficiency towards the photodegradation of a toxic textile dye, rhodamine B, than pristine MgO and commercially available Degussa P25 titania nanoparticles as well as other composites. Under solar irradiation, Fe/MgO-rGO (500) nanocomposite exhibited 86% degradation of rhodamine B dye and generated almost four times higher H2 via photocatalytic water splitting compared to commercially available P25 titania nanoparticles. This promising photocatalytic ability of the Fe/MgO-rGO(500) nanocomposite can be attributed to the improved morphological and surface features due to heat treatment at inert atmosphere as well as escalated charge carrier separation with increased light absorption capacity imputed to rGO incorporation.

Abstract

Lead-free metal halide perovskites have attracted great attention as light harvesters due to their promising optoelectronic and photovoltaic properties. In this investigation, we have successfully synthesized thermally stable cubic phase cesium tin chloride (CsSnCl₃) perovskite nanocrystals with improved surface morphology by adopting a rapid hot-injection technique. The excellent crystalline quality of these cubic shaped nanocrystals was confirmed by high-resolution transmission electron microscopy imaging. The binding of organic ligands on the surface of the sample was identified and characterized using nuclear magnetic resonance spectroscopy. UV-visible spectroscopy confirmed that the CsSnCl₃ nanocrystals have a direct band gap of ∼2.98 eV, which was further confirmed using steady-state photoluminescence spectroscopy. The band edge positions calculated using the Mulliken electronegativity approach predicted the potential photocatalytic capability of the as-prepared nanocrystals, which was then experimentally corroborated through the photodegradation of rhodamine-B dye under both visible and UV-visible irradiation. Our theoretical calculations employing experimentally obtained structural parameters within the generalized gradient approximation (GGA) and GGA+U methods demonstrated a 90% accurate estimation of the experimentally observed optical band gap when U_eff = 6 eV was considered. The ratio of the effective mass of the hole and electron expressed as  was also calculated for U_eff = 6 eV. Based on this theoretical calculation and experimental observation of the photocatalytic performance of CsSnCl₃ nanocrystals, we have proposed a rational interpretation of the “D” value. We think that a “D” value of either much smaller or much larger than 1 is an indication of the low recombination rate of the photogenerated electron–hole pairs and the high photocatalytic efficiency of the photocatalyst. We believe that this comprehensive investigation might be helpful for the large-scale synthesis of thermally stable cubic CsSnCl₃ nanocrystals and also for a greater understanding of their potential in photocatalytic, photovoltaic and other prominent optoelectronic applications.

Abstract

We synthesized strontium titanate SrTiO₃ (STO), Zr doped Sr_1−xZr_xTiO₃ and (Zr, Ni) co-doped Sr_1−xZr_xTi_1−yNi_yO₃ samples using solid-state reaction technique to report their structural, electrical, and magnetic properties. The cubic Pm-3m phase of the synthesized samples has been confirmed using Rietveld analysis of the powder X-ray diffraction pattern. The grain size of the synthesized materials was reduced significantly due to Zr doping as well as (Zr, Ni) co-doping in STO. The chemical species of the samples were identified using energy-dispersive X-ray spectroscopy (EDX). The Zr and Ni dopants’ homogeneity were confirmed from EDX mapping to negate spurious ferroic order due to dopant segregation. We observed forbidden first-order Raman scattering at 148, 547 and 797 cm⁻¹ which may indicate nominal loss of inversion symmetry in cubic STO. The absence of absorption at 500 cm⁻¹ and within 600–700 cm⁻¹ band in Fourier Transform Infrared spectra corroborates Zr and Ni as substitutional dopants in our samples. Due to 4% Zr doping in Sr_0.96Zr_0.04TiO₃ sample dielectric constant, remnant electric polarization, remnant magnetization, and coercivity were increased. Notably, in the case of 4% Zr and 10% Ni co-doping we have observed clearly the existence of both FE and FM hysteresis loops in the Sr_0.96Zr_0.04Ti_0.90Ni_0.10O₃ sample. In this co-doped sample, the remnant magnetization and coercivity were increased by ∼1 and ∼2 orders of magnitude respectively as compared to those of undoped STO. The coexistence of FE and FM orders in (Zr, Ni) co-doped STO might have the potential for interesting multiferroic applications.

Abstract

We report the effect of temperature on the crystallographic structure and magnetic properties of ultrasonically prepared nanostructured Nd_0.7Sr_0.3MnO₃ perovskite manganite. The crystal structure of as-synthesized nanoparticles remains unaltered over a wide scanning temperature range. Temperature dependent magnetization measurements demonstrate that the Curie temperature (T_c) of Nd_0.7Sr_0.3MnO₃ nanoparticles is in the range of 211 K–220 K under largely varying applied magnetic fields. Below T_c, the soft ferromagnetic nature of these nanoparticles is confirmed by the field-dependent magnetization measurements. The absence of the charge-ordered state is also revealed in this nanomanganite down to 20 K, which is strikingly different from analogous Nd–Sr based nanocrystals. The experimentally observed effective paramagnetic moment and saturation magnetic moment have matched quite well with the values calculated theoretically. The T_c values up to a temperature of 220 K, nearly perfect ferromagnetically ordered Mn ions below T_c, high saturation magnetization, and magnetic softness of synthesized nanostructured Nd_0.7Sr_0.3MnO₃ manganite can be associated with their good crystallinity as well as the nominal internal and surface disorder effect owing to intermediate particle size (∼75 nm to 150 nm). Our investigation elucidates the promising potential of nanocrystalline Nd_0.7Sr_0.3MnO₃ particles for numerous technological applications.

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In this investigation, multiferroic bulk ceramic materials with nominal compositions Bi_1-xSm_xFe_1-yTi_yO₃ (x, y = 0.00, 0.03, 0.06) are synthesized by conventional solid-state reaction technique. Their corresponding nanoparticles are fabricated from these bulk powder materials using cost-effective ultrasonication method. Then, the structural and multiferroic properties of the synthesized nanoparticles and their bulk-counterparts are compared. The X-ray diffraction patterns of 6% Sm-Ti co-substituted BiFeO₃ nanoparticles as well as their bulk powder materials confirm rhombohedral to orthorhombic structural phase transition. Dynamic Light Scattering analysis (DLS) demonstrates the formation of particles with a size in the range of 10–100 nm for the 6% Sm-Ti co-substituted BiFeO₃ sample. The fabricated nanoparticles of this particular composition also exhibit suppressed leakage current density and enhanced ferroelectric behavior. These nanoparticles also demonstrate improved ferromagnetic behavior compared to their bulk counterparts. Thus, the present investigation illustrates the impact of Sm and Ti as co-doping elements with 6% concentration in BiFeO₃ nanoparticles with improved structural and multiferroic properties required for practical applications.

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A comprehensive comparison between BiFeO₃-reduced graphene oxide (rGO) nanocomposite and Bi₂₅FeO₄₀-rGO nanocomposite has been performed to investigate their photocatalytic abilities in degradation of Rhodamine B dye and generation of hydrogen by water-splitting. The hydrothermal technique adapted for synthesis of the nanocomposites provides a versatile temperature-controlled phase selection between perovskite BiFeO₃ and sillenite Bi₂₅FeO₄₀. Both perovskite and sillenite structured nanocomposites are stable and exhibit considerably higher photocatalytic ability over pure BiFeO₃ nanoparticles and commercially available Degussa P25 titania. Notably, Bi₂₅FeO₄₀-rGO nanocomposite has demonstrated superior photocatalytic ability and stability under visible light irradiation than that of BiFeO₃-rGO nanocomposite. The possible mechanism behind the superior photocatalytic performance of Bi₂₅FeO₄₀-rGO nanocomposite has been critically discussed.

Abstract

DyCrO₃ and 10% Fe-doped DyCrO₃ nanoparticles have been synthesized using a sol–gel method to investigate their performance in photocatalytic hydrogen production from water. The synthesized nanoparticles have been characterized by performing X-ray diffraction, energy dispersive X-ray spectroscopy and UV-visible spectrophotometric measurements. In addition, field emission scanning electron microscopy has been performed to observe their size and shape. The Fe-doped DyCrO₃ nanoparticles show a significantly smaller band gap of 2.45 eV compared to the band gap of 2.82 eV shown by the DyCrO₃ nanoparticles. The Fe-doped DyCrO₃ nanoparticles show better photocatalytic activity in the degradation of rhodamine B (RhB) compared to the photocatalytic activity shown by both the DyCrO₃ and Degussa P25 titania nanoparticles. The recycling and reuse of Fe-doped DyCrO₃ four times for the photo-degradation of RhB shows that Fe-doped DyCrO₃ is a stable and reusable photocatalyst. To evaluate the extent of the photocatalytic hydrogen production ability of the synthesized nanoparticles, a theoretical model has been developed to determine their “absorptance”, a measure of the ability to absorb photons. Finally, 10% Fe-doped DyCrO₃ proves itself to be an efficient photocatalyst as it demonstrated three times greater hydrogen production than Degussa P25.

Abstract

Gd doped Bi_1-xGd_xMn₂O₅ (x = 0.00–0.12) ceramics are synthesized via solid state reaction technique and they have been investigated for their structural, morphological, magnetic and electric properties. X-ray diffraction experiments and their corresponding Rietveld refinement confirm that the major phase characteristics of all the compositions are orthorhombic. The morphological studies reveal that the average grain size gradually decreases from  to  due to Gd substitution. The temperature dependent zero field cooled (ZFC) and field cooled (FC) magnetization curves demonstrate an antiferromagnetic Néel transition at 42 K. Due to the substitution of 4% Gd, the phase transition remains unaltered, however, both ZFC and FC curves coincide with each other at an applied magnetic field of 500 Oe. The remanent magnetizations and coercive fields are also found to enhance at room temperature due to the substitution of Gd. The polarization vs. electric field hysteresis loops exhibits the ferroelectric behavior of Bi_1-xGd_xMn₂O₅ (x = 0.00–0.12) ceramics at room temperature. Gd substitution also results in enhanced stability of the dielectric constant at wide range of high frequencies with significant suppression of low frequency dispersion particularly for 12% Gd doping. Moreover, a correlation among leakage current, remanent polarization, dielectric constant and microstructure has also been observed while investigating the Gd doped BiMn₂O₅ ceramics.

Abstract

Accurate determination of a material’s optical band gap lies in the precise measurement of its absorption coefficients, either from its absorbance via the Beer–Lambert law or diffuse reflectance spectrum via the Kubelka–Munk function. Absorption coefficients of powder-form nanomaterials calculated from absorbance spectrum do not match those calculated from diffuse reflectance spectrum, implying the inaccuracy of the traditional optical band gap measurement method for such samples. We have modified the Beer–Lambert law and the Kubelka–Munk function with proper approximations for powder-form nanomaterials. Applying the modified method for powder-form nanomaterial samples, both absorbance and diffuse reflectance spectra yield exactly the same absorption coefficients and therefore accurately determine the optical band gap.

Abstract

The manuscript reports the synthesis as well as a comparative investigation of the structural, magnetic, and optical properties between sillenite and perovskite type bismuth ferrite-reduced graphene oxide nanocomposites. Graphite oxide is prepared using the modified Hummers' method, followed by hydrothermal synthesis of bismuth ferrite-reduced graphene oxide nanocomposites at different reaction temperatures. The X-ray diffraction measurements confirm the formation of perovskite type BiFeO₃-rGO nanocomposites at a reaction temperature of 200 °C. This is the lowest temperature to obtain perovskite type BiFeO₃-rGO nanocomposites under the reaction procedure adopted, however, a structural transition to sillenite type Bi₂₅FeO₄₀-rGO is observed at 180 °C. The FESEM images demonstrate that the particle size of the perovskite nanocomposite is 25–60 nm, and for the sillenite phase nanocomposite it is 10–30 nm. The as-synthesized nanocomposites exhibit significantly enhanced saturation magnetization over pure BiFeO₃ nanoparticles, with the sillenite Bi₂₅FeO₄₀-rGO nanocomposite having higher saturation magnetization than perovskite BiFeO₃-rGO. The optical characteristics of the as-synthesized nanocomposites demonstrate considerably higher absorbance in the visible range with significantly lower band gap in comparison to undoped BiFeO₃. Again, the sillenite Bi₂₅FeO₄₀-rGO nanocomposite is shown to have a lower band gap compared to the perovskite counterpart. Our investigation provides a means of selective phase formation as desired between sillenite Bi₂₅FeO₄₀-rGO and perovskite BiFeO₃-rGO by controlling the hydrothermal reaction temperature. The outcome of our investigation suggests that the formation of nanocomposite of sillenite bismuth ferrite with reduced graphene oxide is promising to improve the magnetic and optical properties for potential technological applications.

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Ni_1-xFe_x (x = 0.20, 0.40, and 0.80) alloy nanoparticles (NPs) with tunable magnetization were synthesized by a simple sonofragmentation process, a facile one-step technique to produce NPs directly from bulk powders. The X-ray diffraction (XRD) patterns show the crystalline structure of the alloy samples, and the sizes of the particles are 35 nm from the Scherrer equation. Scanning electron microscopy reveals the aggregation or cluster of spherical NPs with wide size distribution from 20 to 30 nm for all compositions of Ni-Fe nanoalloys. Magnetization versus field curves exhibit superparamagnetic behavior. The saturation magnetization for the Ni_0.80Fe_0.20, Ni_0.60Fe_0.40, and Ni_0.20Fe_0.80 alloy NPs are 57, 66, and 105 emu g^-1, respectively, increasing with Fe content. Such tunability has potential technological applications.

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The synthesis as well as structural, multiferroic and optical characterization of Dy doped BiFeO3 multiferroic ceramic are presented. Bulk polycrystalline Bi_0.9Dy_0.1FeO₃ sample is synthesized by solid state reaction, while their nano counterparts are prepared using ultrasonic probe sonication technique. Significant improvement of phase purity in the as synthesized samples is observed after the doping of Dy both in bulk Bi_0.9Dy_0.1FeO₃ sample and corresponding nanoparticles as evidenced from Rietveld refinement. Magnetization measurements using SQUID magnetometer exhibit enhanced magnetic properties for Dy doped bulk Bi_0.9Dy_0.1FeO₃ ceramic compared to their nanostructured counterparts as well as undoped BiFeO3. Within the applied field range, saturation polarization is observed for Bi_0.9Dy_0.1FeO₃ bulk ceramic only. As a result, intrinsic ferroelectric behavior is obtained just for this sample. Optical bandgap measurements reveal lower bandgap for Dy doped bulk Bi_0.9Dy_0.1FeO₃ ceramic compared to that of corresponding nanoparticles and undoped BiFeO3. The outcome of this investigation demonstrates the potential of Dy as a doping element in BiFeO3 that provides a bulk ceramic material with improved multiferroic and optical properties compared to those of corresponding nanoparticles which involve rigorous synthesis procedure.

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A simple route to prepare Gd_0.7Sr_0.3MnO₃ nanoparticles by ultrasonication of their bulk powder materials is presented in this article. For comparison, Gd_0.7Sr_0.3MnO₃ nanoparticles are also prepared by ball milling. The prepared samples are characterized by x-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive x-ray (EDX), x-ray photoelectron spectroscope (XPS), and superconducting quantum interference device (SQUID) magnetometer. XRD Rietveld analysis is carried out extensively for the determination of crystallographic parameters and the amount of crystalline and amorphous phases. FESEM images demonstrate the formation of nanoparticles with average particle size in the range of 50–100 nm for both ultrasonication and 4 h (h) of ball milling. The bulk materials and nanoparticles synthesized by both ultrasonication and 4 h ball milling exhibit a paramagnetic to spin-glass transition. However, nanoparticles synthesized by 8 h and 12 h ball milling do not reveal any phase transition, rather show an upturn of magnetization at low temperature. The degradation of the magnetic properties in ball milled nanoparticles may be associated with amorphization of the nanoparticles due to ball milling particularly for milling time exceeding 8 h. This investigation demonstrates the potential of ultrasonication as a simple route to prepare high crystalline rare-earth based manganite nanoparticles with improved control compared to the traditional ball milling technique.

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Sr-substituted perovskites, La_1.8Sr_0.2MMnO₆ (M = Ni, Co), were synthesized using the solid-state reaction technique to present a systematic study on their morphological, structural and magnetic properties. The average grain size of the as-prepared La_1.8Sr_0.2MMnO₆ samples are in the range of 0.2–0.7 µm and those for La_1.8Sr_0.2CoMnO₆ manganites are 0.1–2.8 μm, which is significantly less than that of unsubstituted La₂NiMnO₆ (LNMO) and La₂CoMnO₆ (LCMO) manganites. The XPS analysis enlightened about phase purity, binding energy and oxygen vacancy of La_1.8Sr_0.2MMnO₆ manganites. The Sr-substituted LNMO has revealed a sharp ferromagnetic to paramagnetic phase transition at 160 ± 2 K, which is about 120 K less than that of parent LNMO. The Sr-substituted LCMO exhibited such a transition at 220 ± 2 K, which is 8 K less than that of parent LCMO. The temperature-dependent magnetization measurements suggest that the effect of Sr on the transition temperature in LNMO is more significant than that of LCMO.

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In this investigation, undoped BiFeO₃, Gd doped Bi_0.9Gd_0.1FeO₃, and Gd-Ti co-doped Bi_0.9Gd_0.1Fe_1-xTi_xO₃ (x = 0.10, 0.20) materials were synthesized to report their multiferroic properties. The structural analysis and phase identification of these multiferroic ceramics were performed using Rietveld refinement. The Rietveld analysis has confirmed the high phase purity of the 10% Gd-Ti co-doped Bi_0.9Gd_0.1Fe_0.9Ti_0.1O₃ sample compared to that of other compositions under investigation. The major phase of this particular composition is of rhombohedral R3c type structure (wt% >99%) with negligible amount of impurity phases. In terms of characterization, we address magnetic properties of this co-doped ceramic system by applying substantially higher magnetic fields than that applied in previously reported investigations. The dependence of temperature and maximum applied magnetic fields on their magnetization behavior have also been investigated. Additionally, the leakage current density has been measured to explore its effect on the ferroelectric properties of this multiferroic system. The outcome of this investigation suggests that the substitution of 10% Gd and Ti in place of Bi and Fe, respectively, in BiFeO₃ significantly enhances its multiferroic properties. The improved properties of this specific composition is associated with homogeneous reduced grain size, significant suppression of impurity phases and reduction in leakage current density which is further asserted by polarization vs. electric field hysteresis loop measurements.

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In this investigation, Gd and Mn co-doped Bi_0.85Gd_0.15Fe_1−xMn_xO₃ (x = 0.0–0.15) nanoparticles have been prepared to report the influence of co-substitution on their structural, optical, magnetic and electrical properties. Due to simultaneous substitution of Gd and Mn in BiFeO₃, the crystal structure has been modified from rhombohedral (R3c) to orthorhombic (Pn2₁a) and the FeOFe bond angle and FeO bond length have been changed. For Mn doping up to 10% in Bi_0.85Gd_0.15Fe_1−xMn_xO₃ nanoparticles, the saturation magnetization (M_s) has been enhanced significantly, however, for a further increase of doping up to 15%, the M_shas started to reduce again. The co-substitution of Gd and Mn in BiFeO₃nanoparticles also demonstrates a strong reduction in the optical band gap energy and electrical resistivity compared to that of undoped BiFeO₃.

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The ceramic pellets of the nominal compositions Bi_0.7Ba_0.3Fe_1−x Ti _x O₃ (x  =  0.00–0.20) were prepared initially by standard solid state reaction technique. The pellets were then ground into micrometer-sized powders and mixed with isopropanol in an ultrasonic bath to prepare nanoparticles. The x-ray diffraction patterns demonstrate the presence of a significant number of impurity phases in bulk powder materials. Interestingly, these secondary phases were completely removed due to the sonication of these bulk powder materials for 60 minutes. The field and temperature dependent magnetization measurements exhibited significant difference between the magnetic properties of the bulk materials and their corresponding nanoparticles. We anticipate that the large difference in the magnetic behavior may be associated with the presence and absence of secondary impurity phases in the bulk materials and their corresponding nanoparticles, respectively. The leakage current density of the bulk materials was also found to suppress in the ultrasonically prepared nanoparticles compared to that of bulk counterparts.

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Improvement in magnetic and electrical properties of multiferroic BiFeO₃ in conjunction with their dependence on particle size is crucial due to its potential applications in multifunctional miniaturized devices. In this investigation, we report a study on particle size dependent structural, magnetic and electrical properties of sol-gel derived Bi_0.9Ba_0.1FeO₃nanoparticles of different sizes ranging from ∼ 12 to 49 nm. The substitution of Bi by Ba significantly suppresses oxygen vacancies, reduces leakage current density and Fe²⁺ state. An improvement in both magnetic and electrical properties is observed for 10 % Ba-doped BiFeO₃ nanoparticles compared to its undoped counterpart. The saturation magnetization of Bi_0.9Ba_0.1FeO₃ nanoparticles increase with reducing particle size in contrast with a decreasing trend of ferroelectric polarization. Moreover, a first order metamagnetic transition is noticed for ∼ 49 nm Bi_0.9Ba_0.1FeO₃ nanoparticles which disappeared with decreasing particle size. The observed strong size dependent multiferroic properties are attributed to the complex interaction between vacancy induced crystallographic defects, multiple valence states of Fe, uncompensated surface spins, crystallographic distortion and suppression of spiral spin cycloid of BiFeO₃.

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Néel walls in soft magnetic NiFe/NiFeGa hybrid stripe structures surrounded by a NiFe film are investigated by high-resolution Lorentz transmission-electron-microscopic imaging. An antiparallel orientation of magnetization in 1000-nm-wide neighboring unirradiated-irradiated stripes is observed by forming high-angle domain walls during magnetization reversal. Upon downscaling the stripe structure size from 1000 to 200 nm, a transition from a discrete domain pattern to an effective magnetic medium is observed for external magnetic-field reversal. This transition is associated with the vanishing ability of hosting high-angle domain walls between adjacent stripes.

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The exchange bias (EB) effect has been observed in magnetic Bi_0.9Gd_0.1Fe_0.9Ti_0.1O₃ nanoparticles. The influence of magnetic field cooling on the exchange bias effect has also been investigated. The magnitude of the exchange bias field (H_EB) increases with the cooling magnetic field, showing that the strength of the exchange bias effect is tunable by the field cooling. The H_EB values are also found to be dependent on the temperature. This magnetically tunable exchange bias obtained at temperatures up to 250 K in Bi_0.9Gd_0.1Fe_0.9Ti_0.1O₃ nanoparticles may be worthwhile for potential applications.

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Using a focused-ion-beam microscope, we create nontopographic features that provide controlled modification of domain-wall structure, size, and pinning strength in 500-nm-wide nanowires composed from Cr⁡(3  nm)/permalloy⁡(10  nm)/Cr⁡(5  nm). The pinning sites consist of linear defects where magnetic properties are modified by a Ga⁺-ion probe of diameter ∼ 10  nm. Detailed studies of the structural, chemical, and magnetic changes induced by the irradiation, which show the modified region to be ∼40–50  nm wide, are performed using scanning-transmission-electron-microscopy modes of bright-field imaging, electron-energy-loss spectroscopy, and differential-phase-contrast imaging on an aberration corrected (Cs) instrument. The Fresnel mode of Lorentz-transmission-electron microscopy is used for studies of domain-wall behavior, where we observe changes in depinning strength and structure with irradiation dose and line orientation. We present an understanding of this behavior based upon micromagnetic simulation of the irradiated defects and their effect on the energy terms for the domain walls.

Abstract

𝑍⁢𝑛⁢𝐶⁢𝑟₂⁢𝑂₄ compound is well Known to show the frustration of the spin structure. At 12 K, 𝑍⁢𝑛⁢𝐶⁢𝑟₂⁢𝑂₄ distorts to break symmetry of the degenerated frustrated spin states by the spin-Peierls-like phase transition, accompanying with the antiferromagnetic ordering. On the other hand, 𝑁⁢𝑖⁢𝐶⁢𝑟₂⁢𝑂₄ undergoes a Jahn–Teller phase transition at a temperature of 310 K, differing from the low temperature ferrimagnetic transition temperature 𝑇𝑐 of about 60 K. It is also reported that 𝑁⁢𝑖⁢𝐶⁢𝑟₂⁢𝑂₄ shows another magnetic phase transition at about 30 K. These two phase transitions accompanying with the lattice change can be understood by the magneto-elastic interactions. Two interactions, the Jahn–Teller interaction and the spin-Peierls-like interaction are co-exist in 𝑁⁢𝑖_𝑥⁢𝑍⁢𝑛_1−𝑥⁢𝐶⁢𝑟₂⁢𝑂₄ system. In this report the 𝑁⁢𝑖_𝑥⁢𝑍⁢𝑛_1−𝑥⁢𝐶⁢𝑟₂⁢𝑂₄ compounds with x = 0.8, 0.6 and 1 are investigated by the X-ray diffraction measurements. From these measurements the crystal structures are determined. The full width at half maximum and integrated intensity give the fruitful information for magnetic elastic interactions.

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We present a simple technique to synthesize ultrafine nanoparticles directly from bulk multiferroic perovskite powder. The starting materials, which were ceramic pellets of the nominal compositions Bi_0.9Gd_0.1Fe_1−xTi_xO₃ (x = 0.00–0.20), were prepared initially by a solid state reaction technique, then ground into micrometer-sized powders and mixed with isopropanol or water in an ultrasonic bath. The particle size was studied as a function of sonication time with transmission electron microscopic imaging and electron diffraction that confirmed the formation of a large fraction of single-crystalline nanoparticles with a mean size of 11–13 nm. A significant improvement in the magnetic behavior of Bi_0.9Gd_0.1Fe_1−xTi_xO₃ nanoparticles compared to their bulk counterparts was observed at room temperature. This sonication technique may be considered as a simple and promising route to prepare ultrafine nanoparticles for functional applications.

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Room temperature dielectric and magnetic properties of BiFeO₃ samples, co-doped with magnetic Gd and non-magnetic Ti in place of Bi and Fe, respectively, were reported. The nominal compositions of Bi_0.9Gd_0.1Fe_1–xTi_xO₃ (x = 0.00-0.25) ceramics were synthesized by conventional solid state reaction technique. X-ray diffraction patterns revealed that the substitution of Fe by Ti induces a phase transition from rhombohedral to orthorhombic at x > 0.20. Morphological studies demonstrated that the average grain size was reduced from ∼1.5 μm to ∼200 nm with the increase in Ti content. Due to Ti substitution, the dielectric constant was stable over a wide range of high frequencies (30 kHz to 20 MHz) by suppressing the dispersion at low frequencies. The dielectric properties of the compounds are associated with their improved morphologies and reduced leakage current densities probably due to the lower concentration of oxygen vacancies in the compositions. Magnetic properties of Bi_0.9Gd_0.1Fe_1–xTi_xO₃ (x = 0.00-0.25) ceramics measured at room temperature were enhanced with Ti substitution up to 20% compared to that of pure BiFeO₃ and Ti undoped Bi_0.9Gd_0.1FeO₃ samples. The enhanced magnetic properties might be attributed to the substitution induced suppression of spiral spin structure of BiFeO₃. An asymmetric shifts both in the field and magnetization axes of magnetization versus magnetic field curves was observed. This indicates the presence of exchange bias effect in these compounds notably at room temperature.

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We demonstrate that for multilayered magnetic nanowires, where the thickness and composition of the individual layers have been carefully chosen, domain walls can be pinned at non-topographic sites created purely by ion irradiation in a focused ion beam system. The pinning results from irradiation induced alloying leading to magnetic property modification only in the affected regions. Using Lorentz transmission electron microscopy, we have studied the pinning behavior of domain walls at the irradiation sites. Depending on the irradiation dose, a single line feature not only pinned the domain walls but also acted to control their structure and the strength of their pinning.

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Nominally identical permalloy nanowires, with widths down to 150 nm, were fabricated onto a single-electron transparent Si₃N₄ membrane using electron beam lithography (EBL) and focused ion beam (FIB) milling. Transmission electron microscopy (TEM) experiments were performed to compare the nanostructures produced by these two techniques in what we believe is the first direct comparison of fabrication techniques for nominally identical nanowires. Both EBL and FIB methods produced high quality structures with edge roughness being of the order of the mean grain size 5–10 nm observed in the continuous films. However, significant grain growth was observed along the edges of the FIB patterned nanowires. Lorentz TEM in situ imaging was carried out to compare the magnetic behavior of the domain walls in the patterned nanowires with anti-notches present to pin domain walls. The overall process of domain wall pinning and depinning at the anti-notches showed consistent behavior between nanowires fabricated by the two methods with the FIB structures having slightly lower characteristic fields compared to the EBL wires. However, a significant difference was observed in the formation of a vortex structure inside the anti-notches of the EBL nanowires after depinning of the domain walls. No vortex structure was seen inside the anti-notches of the FIB patterned nanowires. Results from micromagnetic simulations suggest that the vortex structure inside the anti-notch can be suppressed if the saturation magnetization (⁠⁠M_s) is reduced along the nanowire edges. A reduction of M_s along the wire edges may also be responsible for a decrease in the domain wall depinning fields. Whereas the two fabrication methods show that well-defined structures can be produced for the dimensions considered here, the differences in the magnetic behavior for nominally identical structures may be an issue if such structures are to be used as conduits for domain walls in potential memory and logic applications.

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In this paper, a systematic investigation of the microstructure, high performance magnetic hardness as well as novel magnetic memory effect of the Pr₄Fe₇₆Co₁₀B₆Nb₃Cu₁ nanocomposite magnet fabricated by conventional melt-spinning followed by annealing at temperatures ranging from 600 to 700 °C in Ar gas for nanocrystallization are presented and discussed. Transmission electron microscopy (TEM) observation confirms an ultrafine structure of bcc-Fe(Co) as a magnetically soft phase and Pr₂Fe₁₄B as a hard magnetic phase with a spring-exchange coupling in order to form the nanocomposite state. Electron diffraction analysis also indicates that the Co atoms together with Fe atoms form the Fe₇₀Co₃₀ phase with a very high magnetic moment (2.5 μ_B), leading to a high saturation magnetization of the system. High magnetic hardness is obtained in the optimally heat-treated specimen with coercivity H_c = 3.8 kOe, remanence B_r = 12.0 kG, M_r/M_s = 0.81 and maximum energy product (BH)_max = 17.8 MG Oe, which is about a 25% improvement in comparison with recent results for similar compositions. High remanence and reduced remanence are the key factors in obtaining the high performance with low rare-earth concentration (only 4 at.%). High-resolution TEM analysis shows that there is a small amount of residual amorphous phase in the grain boundary, which plays a role of interphase to improve the exchange coupling. Otherwise, in terms of magnetic after-effect measurement, a magnetic memory effect was observed for the first time in an exchange-coupled hard magnet.

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Bulk polycrystalline layered perovskite sample La₂Sm_0.4Sr_0.6Mn₂O₇ was prepared by the conventional solid-state reaction technique. Temperature dependence of magnetization measurements in the zero-field-cooled and field-cooled conditions with an applied magnetic field of 100 Oe indicates that layered manganite La₂Sm_0.4Sr_0.6Mn₂O₇ undergoes a paramagnetic to ferromagnetic transition at Curie temperature T_c∼355 K. The magnetic transition temperature (T_c) is much higher than metal–insulator transition temperature (T_p) obtained from temperature dependence resistivity measurement. The anisotropic exchange interaction may be one of the reasons resulting in a large deviation between T_c and T_p. Field dependence of magnetization measurements showed a high value of magnetization (62 emu/g at 5 K and 42 emu/g at 300 K) in an applied magnetic field of 1 T. At 78 K, a sharp increase of magnetoresistance was observed at low magnetic fields followed by a weak and linear dependence at high fields.

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A series of bulk polycrystalline layered perovskite manganites La_n−nxCa_1+nxMn_n−yCr_yO_3n+1 (n=2, 3; x=0.3; y=0.075, 0.15, 0.3) are prepared by conventional solid-state reaction technique and the effect of MnO₂ layers on their transport properties are studied. Powder X-ray diffraction (XRD) patterns of the samples indicate their single-phase character. Metal–insulator (MI) transition is observed in both Cr-doped and undoped samples. There is a systematic change of MI transition temperature with the increase of Cr concentration. Results on the transport properties of these samples have indicated methodical variations in a number of features like electrical resistivity, MI transition, low-field magnetoresistance, etc. with the number of MnO₂ layers. A regular variation of different features is also observed when Mn site is substituted by Cr.

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Bulk layered perovskite samples La₂Sm_xSr_1-xMn₂O₇ (x = 0.4, 0.6 and 0.8) were prepared by the conventional solid-state reaction technique and their temperature dependence of electrical resistance and magnetization measurements were performed. The metal-insulator (M-I) transition, magnetic phase transition and the colossal magnetoresisitance phenomena were observed. The M-I transition peak temperature (T_p) shifts towards lower temperature with increasing x while magnetic field shifts T_p to the high temperature regime. Experimental results show that layered manganites La₂Sm_xSr_1-xMn₂O₇ (x = 0.4, 0.6 and 0.8) exhibit ferromagnetic-to-paramagnetic transitions at Curie temperature T_c ~ 355, 286 and 277 K for x = 0.4, 0.6 and 0.8, respectively. A large deviation between the metal-insulator transition and the magnetic transition temperature is observed for all the doping concentrations. But in the case of well-known ABO₃ type perovskite manganites like La_0.75Ca_0.25MnO₃, the M-I transition was found previously very close to magnetic transition. At 78 K, a sharp increase of magnetoresistance was observed at low magnetic fields.

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Magnetoresistive properties of Gd doped various polycrystalline samples of Ruddlesden -Popper series (La_1-xSr_x)_n+1Mn_nO_3n+1 (n = 2) sintered at temperature 11000C for 24 hours in air have been investigated from room temperature down to liquid nitrogen temperature using standard four-probe technique. X-ray diffraction pattern have confirmed the single phase structure of all the samples with no significant trace of impurity. Sample La_1.4Sr_1.6Mn₂O₇ shows a Metal-Insulator (M-I) transition with a peak in the electrical resistivity at temperature Tp ~ 134 K and 117 K with an applied magnetic field of 0.86 and O Tesla, respectively. Replacement of La by small amount of Gd atoms in this compound is found to lower the ferromagnetic (or metal-insulator) transition temperature, an effect which would be due to bond bending caused by the lattice adjusting to the size differential between the La and Gd ions. On the contrary, normalized resistivity behavior as a function of temperature for samples La_1.0Gd_0.4 Sr_1.6Mn₂O_7, La_1.0Gd_0.6Sr_1.4Mn₂O₇, and La_1.0Gd_0.8Sr_1.2Mn₂O₇ in zero field and in an applied magnetic field of 0.86 T reveal that when non-magnetic Sr is replaced with magnetic Gd atom the transition temperature increases dramatically favoring metallic phase. The magnetic property of Gd atom might be responsible for higher transition temperature. Increase in magnetoresistance at lower field is observed to be faster than at higher field. For example, sample of La_1.4Sr_1.6 Mn₂O₇ exhibited 15% magnetoresistance (MR) at an applied magnetic field of 0.13 T whereas the MR of 19% has been obtained for this sample upon the application of 0.86 T magnetic field. All the other compounds exhibited similar behavior. The exhibited large MR effects in this compound at low temperature and very low field might be associated with magnetic-domain based scattering or spin-polarized tunneling between grains.

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