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, 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

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, 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

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 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 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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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 BiFeO₃nanoparticles 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 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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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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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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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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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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