BiFeO3 Research Articles

Synthesis of Na0.02Bi0.98FeO3-δ through the standardized preparation of BiFeO3

This research describes the synthesis of the ferroelectric perovskite Na0.02Bi0.98FeO3-δ using a low-cost solid-state method starting from a bismuth ferrite BiFeO3 structure in order to obtain a material with improved properties for photovoltaic applications. The synthesized materials were characterized by X-ray Diffraction (XRD) technique to determine the effective synthesis conditions for six undoped BiFeO3 samples obtained at different calcination temperatures and quantified by Rietveld® refinement of diffraction patterns, finding homogeneous phase formation at 810 °C under laboratory conditions. The effective synthesis temperature allowed obtaining a stable perovskite-type material, doped with Na+ and its structural characterization by XRD showed a structural modification in the unit cell with respect to BiFeO3 due to the incorporation of sodium cation. The binding energies determined by X-ray photoelectron spectroscopy (XPS) confirmed the formation of the main crystalline phase and the insertion of Na+ cations inside perovskite structure. The morphological characterization by scanning electron microscopy (SEM) of the synthesized material showed the formation of two stable morphologies: Bi2Fe4O9 and Na0.02Bi0.98FeO3-δ as the predominant phase. The optical characterization by Raman spectroscopy allowed identifying variations in the vibration modes of the perovskite doped with respect to undoped bismuth ferrite. The variation of the optical bandgap was determined using the Tauc’s equation and the electrical characterization by solid state electrochemical impedance spectroscopy (SS-EIS) demonstrated an increase in electrical conductivity, at room temperature, by the Na+ doped perovskite, proving an optimal behavior for its potential uses as a semiconductor. The results indicate that the current methodology is promising for the low-cost production of Na0.02Bi0.98FeO3-δ type perovskites for photovoltaic applications.

A magnetite catalysed heterogeneous solar photo electro-Fenton system enhanced with lanthanum doped bismuth ferrite photoanode for the degradation of aspirin in water

The effect of photoanode on a solar photo electro-Fenton system (SPEF) consisting of a magnetite nanoparticle catalyst impregnated carbon felt cathode is studied by coupling the SPEF system to a lanthanum-doped bismuth ferrite (La-BFO) photoanode. The resulting system, referred to as La-BFO /SPEF, was used in the degradation of acetyl salicylic acid in wastewater. The synthesised La-doped/undoped BFO photoanodes and magnetite nanoparticles were characterised with SEM, XRD and FTIR. The heterogeneous electro-Fenton system was prepared by attaching the magnetite nanoparticle to a carbon felt electrode through magnetisation. The effects of La dopant concentration in the photoanode material (doped and undoped BFO on a fluorine doped tin oxide substrate), pH values, current density and anodic oxidation contribution to the SPEF system were explored through parameters such as total organic carbon (TOC) measurements and mineralization current efficiency. A TOC removal of 68 % and 54 % was recorded for the La-doped photoanode (La-BFO/SPEF) and undoped system (BFO/SPEF) respectively, thus reflecting the contribution from the band gap tuning of the photoanode material. The predominant species in the degradation of acetyl salicylic acid were deduced by radical scavenging experiments. The coupling approach and the irradiation with visible light, enhanced the overall performance of the degradation system.

Spin Hall Magnetoresistance in Pt/BiFeO3 Bilayer

Multiferroic materials are general antiferromagnets with negligibly small net magnetization, which strongly limits their magnetoelectric applications in spintronics. Spin Hall magnetoresistance (SMR) is sensitive to the orientation of the Néel vector, which can be applied for the detection of antiferromagnetic states. Here, we apply SMR on the unique room-temperature antiferromagnetic multiferroic material BiFeO3 (BFO). The angular dependence of SMR in a bilayer of epitaxial BFO (001) and heavy metal Pt is studied. By rotating the sample under a magnetic field of 80 kOe in the film plane, the resistance shows the maximum when the field is perpendicular to the current while it shows the minimum when the field is along the current. This can be well explained by the SMR in the bilayer of heavy metal/antiferromagnet with the relative orientation between the Néel vector and current direction. In contrast, the angular dependence of the resistance of Pt directly deposited on a SrTiO3 (001) substrate shows a 90° shift with the magnetic field rotating in the film plane, which originates from the Hanle magnetoresistance of Pt. The obtained spin mixing conductance at the Pt/BFO interface clearly confirms the efficient spin transmission. Our results provide a possible solution for applications of antiferromagnetic multiferroic materials in spintronics.

Structural, Dielectric and Impedance Phenomena in Copper Ferrite Nano Powders for Hydroelectric Cell Application

Multiferroic materials have become the new era of research because it exhibits the presence of more than two ferroic orderings in its same phase. The pure copper ferrite nano powders have been prepared using sol-gel auto combustion method. The particle size is found to be near about 30-40 nm. Pure copper ferrite nanoparticles have been chosen to prepare because of its improved dielectric and structural properties. The sharpened peaks obtained from the XRD diffraction pattern confirms the crystalline nature of the sample. The structural and impedance studies of pure copper ferrites has also been reported. The SEM analysis confirms the formation of nanoparticles by revealing the value of grain size in nanometer range. The dielectric studies exhibit the Maxwell Wagner polarization and impedance spectroscopy confirms the contribution in conductivity from both grains and grain boundaries at room temperature. The fabrication of hydroelectric cell having area=0.75 cm2 has been done using pure copper ferrite nanoparticles which have shown improved value of current in wet state as compared to other ferrites like cobalt ferrites and bismuth ferrites. These all properties are responsible for improving the structural stability and thus this material can be suggested for fabricating the hydroelectric cells.

Facile synthesis, characterization, and photocatalytic performance of Bi1-xLaxFeO3 (0 ≤ x ≤ 0.25) perovskite nanoparticles

In this study, we report the combustion-based synthesis and characterization of La-substituted BiFeO3 (BFO) perovskite nanoparticles. Undoped BFO NPs (x = 0) were found to have a single perovskite phase with a rhombohedral structure, while La-BFO NPs (x = 0.05 to 0.25) with Bi3+, La3+, Fe2+, and O2– ions species showed an average crystalline size (≈ 16–22 nm increase) and a reduced band gap. Morphological analyses revealed that La-BFO NPs have an irregular shape, with a propensity towards aggregation and the formation of fused grains with well-defined grain boundaries. The magnetization-field hysteresis curves demonstrated that La-BFO NPs exhibit ferromagnetic behavior at ambient temperature. The surface alterations were assessed using the Zeta potential, and it was discovered that the La-doping BFO perovskite system can generate a negative shift in the flat-band potential. Furthermore, the photocatalytic degradation (PCD) of rhodamine B by La-BFO NPs in the presence of visible light was investigated. When a little amount of H2O2 was added during photocatalysis, La-BFO NPs demonstrated photo-Fenton-like catalytic activity, leading to 99.50% PCD efficiencies.

Subnanosecond Reconfiguration of Ferroelectric Domains in Bismuth Ferrite.

Domain switching is crucial for achieving desired functions in ferroic materials that are used in various applications. Fast control of domains at subnanosecond timescales remains a challenge despite its potential for high-speed operation in random-access memories, photonic, and nanoelectronic devices. In this work, ultrafast laser excitation is shown to transiently melt and reconfigure ferroelectric stripe domains in multiferroic bismuth ferrite on a timescale faster than 100ps. This dynamic behavior is visualized by picosecond- and nanometer-resolved X-ray diffraction measurements as well as time-resolved X-ray diffuse scattering. The disordering of stripe domains is attributed to the screening of depolarization fields by photogenerated carriers resulting in the formation of charged domain walls, as supported by phase field simulations. Furthermore, the recovery of disordered domains exhibits subdiffusive growth on nanosecond timescales, with a nonequilibrium domain velocity reaching up to 10 m/s. These findings present a new approach to image and manipulate ferroelectric domains on subnanosecond timescales, which can be further extended into other photoferroic systems to modulate their electronic, optical, and magnetic properties beyond GHz frequencies. This approach could pave the way for high-speed ferroelectric data storage, computing and photonic applications in a range of photoferroics, and, more broadly, defines new approaches for visualizing the non-equilibrium dynamics of heterogeneous and disordered materials. This article is protected by copyright. All rights reserved.

Enhancing Photocatalytic Activity of Bismuth Ferrite (BiFeO3) via Gadolinium and Copper Doping: A Sol-Gel Synthesis and Characterization Study

In this current research work, the sol-gel method was employed to synthesise, characterize and evaluate the photocatalytic activity of bismuth ferrite (BiFeO3, BFO) doped with two distinctive components consisting of a rare earth element Gadolinium (Gd) and a transition metal Copper (Cu). The dopant concentrations were systematically varied with different weight percentages (wt.%) denoted as Bi1-xGdxFe1-yCuyO3 (where ‘x’ = 0.10, 0.15 and 0.20 wt.%, where ‘y’ = 0.05, 0.10, and 0.15 wt.%). Subsequently, characterizations of the prepared samples were conducted using an array of cutting-edge analytical techniques including X-ray diffraction (XRD), filed emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDAX), and transmission electron microscopy (TEM). The XRD analysis results indicated that the presence of small impurity peaks was found in both Gd-doped BFO and GdCu-doped BFO. The FE-SEM and TEM results provided confirmation that the material was observed as a spherical shape, and the elemental compositions were also confirmed through EDAX analysis. The photocatalytic degradation of Rhodamine B dye under the influence of visible light irradiation was carried out and the results revealed varying degradation times, specifically, for Gd and Cu-doped BFO (Gd and Cu = 0.1 wt.%) achieved almost 98% degradation occurred in 30 minutes.

Cation substitution and size confinement effects on structure, magnetism and magnetic hyperthermia of BiFeO3-based multiferroic nanoparticles and hydrogels

Highly crystalline BiFeO3 (BFO), Bi0.97Sm0.03FeO3 and BiFe0.97Co0.03O3 nanoparticles are synthesized via the chemical co-precipitation method after calcination at 600 °C in air for 2 h. The effect of cation substitution, Sm for Bi and Co for Fe, on the structural and magnetic properties of BFO nanoparticles is investigated, whereas their magnetically induced heating efficiency in radio frequency alternating magnetic fields is examined. X-ray diffraction indicates the formation of the R3c phase in all compounds, while the corresponding Rietveld refinement reveals a variation of the lattice parameters upon doping, suggesting structural distortion within the BFO lattice due to the ionic radii mismatch between doped and host elements. Transmission electron microscopy unveils smaller particle sizes for the doped nanoparticles, owing to the frustrated particle growth induced by the dopants, whose presence is verified by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. The combined effect of cation substitution and size confinement results in the suppression of the spiral spin structure of BFO, leading to the significantly enhanced magnetic features of the doped nanoparticles at room temperature. For possible applications in the biomedical sector, we tested them as heating agents in magnetic hyperthermia. The dispersion of BiFe0.97Co0.03O3 nanoparticles in water at a concentration of 4 mg/mL could reach the therapeutic window of 41–45 °C for cancer treatment in 50 mT at 375 kHz, whereas the remarkable temperature increase of the BFO-based multiferroic hydrogels, under the same conditions, is auspicious for an effective local treatment at reduced toxicity.

Multiferroic behavior of room temperature bismuth ferrite with tailored calcination temperature

One of the few materials that is multiferroic (antiferromagnetic and ferroelectric) is bismuth ferrite. In this study, we used the sol-gel method to create multiferroic bismuth ferrite and examined its structural and optical characteristics. The annealing temperature used to create bismuth ferrite was 600°C. The rhombohedral crystal structure was revealed by X-ray diffraction (XRD) investigation. The XRD diffractogram data examines the phase and planes of orientation for the synthesized materials. The crystalline size for the peak was determined using the Scherrer equation. Analysis using the Fourier transform infrared (FTIR) confirmed the existence of M-O octahedral and tetrahedral coordinates of the M-O bonds formed. The Fourier transform infrared in the wavenumber range of 500–850 cm−1 has been used to study the vibrational modes of the octahedral and tetrahedral metal complexes in the sample. Studies using a FESEM show that the synthesized nanocomposite has morphological characteristics, including interconnected agglomerates with spherical, irregular, or non-uniform elongated forms. By increasing the loading percentage of bismuth ferrite, the composite remnant magnetization (Mr) and saturation magnetization (Ms) values were discovered to be 0.43701 emu/g and 0.1940 emu/g, respectively. A frequency range of 10 Hz to 106 Hz was used to study the dielectric measurement of the nanocomposites. In the temperature range of 310 to 525 K, the AC conductivity has been measured, and it has been discovered that conductivity decreases as temperature rises. A temperature increase results in a reduction in the dielectric constant and dielectric loss. The initial data imply that the nanocomposite is a possible contender for use in capacitors with high dielectric constants. The composite will be useful for usage in hard disc components due to its magnetic characteristics, which is significant.

Effect of Gd and Ce Doped BiFeO3 for Photocatalytic Activity

In this current research work deals with the synthesis, characterization and photocatalytic activity of gadolinium (Gd) and cerium (Ce) doped bismuth ferrite oxide BiFeO3 (BFO). All the samples BFO, BGF-1, BGCF-1, BGCF-2 and BGCF-3 were synthesized by sol-gel method. The structural analysis carried out by X-ray diffraction (XRD), surface morphology examined by field emission scanning electron microscopy (FE-SEM) with EDAX and transmission electron microscopy (TEM), the magnetic properties investigated using vibration sample magnetometer (VSM) and their photocatalytic activity was evaluated by Rhodamine B (RhB) dye under visible light irradiation. The results found that the Gd (0.1 wt.%) and Ce doped (0.1 wt.%) BFO showed better photocatalytic activity as compared to BFO and other samples. HIGHLIGHTS An approach rare earth materials Gd & Ce doping in BiFeO3 Photocatalytic activites and Degradation constants well explained with graphs Gd (0.1 wt%) and Ce (0.1 wt%) doped BiFeO3 showed less photodegradation time than pure BiFeO3 & other doping concentrations Bi9Gd0.1Fe0.9Ce0.1O3 has enhanced photocatalytic degradation for Rhodamine B Degradation of Rhodamine B for the sample BFO is about 50 % and for Gd (0.1 wt%) and Ce (0.1 wt%) doped BiFeO3 is very high that is almost 90 % GRAPHICAL ABSTRACT

Multiferroic properties of BiFeO3 thin films with Ce substitution

In this study, we investigated the crystalline structure, ferroelectricity, leakage current density, magnetic, and nanomechanical properties of BiFeO3 (BFO) films with Ce substitution. Bi1-xCexFeO3 (BCFO) films with x = 0.00, 0.03, 0.06, 0.09, and 0.15 were deposited on glass substrates by using pulsed laser deposition. The experimental results showed that the BCFO films mainly composed the perovskite phase. The structure changed from rhombohedral when x = 0.00 to pseudo-cubic when x = 0.03, and pseudo-cubic phase coexisted with an additional Bi2Fe4O9 phase when x = 0.06–0.09. The BCFO films exhibited improved ferroelectricity and desirable magnetic characteristics. The remanent polarization (2Pr) increased significantly with the Ce concentration, reaching 189.3 μC/cm2 and 100.0 μC/cm2 when x = 0.03 and x = 0.06, respectively, but decreasing at higher Ce contents. The BCFO film with x = 0.03 had a remarkable 2Pr value of 189 μC/cm2 after 108 cycles due to the high (110) texture, fine microstructure, and flat interface resulting in strong anti-fatigue properties. The leakage mechanisms in the BCFO films were also examined. The films exhibited enhanced saturation magnetization (Ms) values ranging from 3.8 to 10.0 emu/cm3, which were attributed to suppression of the spiral spin configuration and the larger magnetic moment associated with the Ce3+ ion. The nanomechanical characteristics of the BCFO films, such as hardness, were significantly influenced by the grain size and phase composition. These findings provide valuable insights into enhancement of the multiferroic properties of BFO polycrystalline films through Ce substitution for use in various applications.

The effect of lanthanides (Er, Gd and La) on the adsorption and photocatalytic performance of bismuth ferrite

The effect of lanthanides (Er, Gd and La) on the adsorption and photocatalytic performance of bismuth ferrite

Self-assembled BiFeO3@MIL-101 nanocomposite for antimicrobial applications under natural sunlight

In this paper, we report on the synthesis of a new hybrid photocatalytic material activated by natural sunlight irradiation. The material consists of multiferroic nanoparticles of bismuth ferrite (BFO) modified through the growth of the Fe-based MIL-101 framework. Material characterization, conducted using various techniques (X-ray diffraction, transmission electron microscopy, FTIR, and X-ray photoelectron spectroscopies), confirmed the growth of the MIL-101 metal–organic framework on the BFO surface. The obtained system possesses the intrinsic photo-degradative properties of BFO nanoparticles significantly enhanced by the presence of MIL-101. The photocatalytic activity of this material was tested in antibacterial experiments conducted under natural sunlight exposure within the nanocomposite concentration range of 100–0.20 µg/ml. The MIL-modified BFO showed a significant decrease in both Minimum Inhibiting Concentration and Minimum Bactericide Concentration values compared to bare nanoparticles. This confirms the photo-activating effect of the MIL-101 modification. In particular, they show an increased antimicrobial activity against the tested Gram-positive species and the ability to begin to inhibit the growth of the four Escherichia coli strains, although at the maximum concentration tested. These results suggest that the new nanocomposite BiFeO3@MOF has been successfully developed and has proven to be an effective antibacterial agent against a wide range of microorganisms and a potential candidate in disinfection processes.

Leakage current characteristics of polycrystalline BiFeO3 thin films affected by thickness-dependent domain wall currents

Polycrystalline BiFeO3 (BFO) thin films with a mixed crystallinity of c-oriented crystallinity and a-oriented crystallinity were deposited on a (200) Pt/TiO2/SiO2/Si substrate to have a thickness of 50, 100, and 150 nm. The ferroelectric domains observed with vertical piezoresponse force microscope (VPFM) and lateral PFM (LPFM) showed a mixed domain structure of c-domains and a-domains, and the ratio of a-domains increased as the thickness increased. The domain wall currents at the a-domains and c-domain boundaries of the BFO thin films were measured by conduction atomic force microscopy (CAFM) experiments and they were larger than those at the c-domains boundaries. In particular, the leakage currents, ferroelectric polarizations, and piezoelectric coefficients of the BFO thin films according to their thickness were significantly affected by the formation of the a-domains.

Structural, Spectroscopic, and Electrical Properties of (Ho, Mn)‐Codoped Bismuth Ferrites Synthesized Through Solid‐State Route

Bismuth ferrites (BiFeO3) are popularly known as BFOs and have potential application at room temperature in present‐day material science and ceramic industry due to their multiferroic and optical properties. Synthesis methods, temperature treatments, and doping are effective for tuning the structural and multiferroic properties of BFO, among which rare earth metals in Bi‐site and transition metals in Fe‐site have shown interesting results. This work explores the synthesis and characterizations of (holmium, manganese)‐codoped BFOs where solid‐state synthesis route and some electrical analyses are the novel studies attempted herein. X‐ray diffraction results explain the structural transition from rhombohedral to mixed‐phase ordering. Grain formation and the elemental concentrations are studied using scanning electron microscopy (SEM) and energy‐dispersive ray spectra (EDAX). Electrical analysis such as dielectric behavior with respect to frequency and temperature impedance analysis is studied in detail. Polarization versus electric field (P–E) hysteresis loop shows the ferroelectric nature of the codoped sample with lossy nature and reduced remnant polarization with doping. The dielectric anomalies with frequency and temperature are analyzed in detail, and antiferromagnetic transition around Neel temperature is discussed.

Carbon nanotubes @Cu/Ni loaded BFO for photothermal catalytic conversion of CO2 by H2O

Bismuth ferrite (FeBiO3, BFO) has excellent photocatalytic activity and a reasonable bandgap width (approximately 2.1 eV), making it a promising material for CO2 catalytic reduction research. In order to enhance the CO2 catalytic reduction performance of BFO, Cu/Ni (molar ratio = 6:5) metal particles were supported on carbon nanotubes (CNTs) at a fixed mass ratio of 38.6% in this study, and it was discovered that adding polyvinylpyrrolidone (PVP) might improve metal particle dispersion. Following that, CNTs @Cu/Ni were supported on hydrothermally produced BFO at mass ratios of 1%, 3%, 5%, and 7% to produce BFO-CNTs @Cu/Ni ternary composites. We investigated its CO2 catalytic reduction capability under photothermal and mild settings and discovered that BFO-3% CNTs @Cu/Ni had the greatest CO2 catalytic conversion efficiency (CH4 yield = 24.2 mol g−1 h−1). This is due to the fact that BFO-CNTs @Cu/Ni have superior light absorption and carrier separation efficiency than pure BFO.

Top electrode dependence of the write-once-read-many-times resistance switching in BiFeO3 films

The electrode is one of the key factors that influences and controls the resistive switching characteristic of a resistive switching device. In this work, we investigated the write-once-read-many-times (WORM)-resistive switching behavior of BiFeO3 (BFO)-based devices with different top electrodes, including Pt, Ag, Cu, and Al. The WORM-resistive switching behavior has been observed in Pt/BFO/LaNiO3 (LNO), Ag/BFO/LNO, and Cu/BFO/LNO devices. In the initial high resistance state, the Pt/BFO/LNO device shows space-charge-limited current conduction due to the large Schottky barrier height at the Pt/BFO interface, while the Ag/BFO/LNO and Cu/BFO/LNO devices exhibit Schottky emission conduction due to the small barrier height at both top electrode/BFO and BFO/LNO interfaces. In the low resistance state, the metallic conduction of the Pt/BFO/LNO device is a result of the formation of conduction filaments composed of oxygen vacancies, and yet the metallic conduction of Ag/BFO/LNO and Cu/BFO/LNO devices is due to the formation of oxygen vacancies-incorporated metal conduction filaments (Ag and Cu, respectively). The observed hysteresis I-V curve of the Al/BFO/LNO device may be attributed to oxygen vacancies and defects caused by the formation of Al–O bond near the Al/BFO interface. Our results indicate that controlling an electrode is a prominent and feasible way to modulate the performance of resistive switching devices.

Fabricating freestanding electrocatalyst with bismuth‐iron dual active sites for efficient ammonia synthesis in neutral media

AbstractElectrocatalytic N2 reduction (NRR) has been regarded as a promising approach for environment‐friendly and sustainable ammonia (NH3) synthesis. However, developing cost‐effective electrocatalysts with high NRR efficiency at low overpotential in neutral media remains a great challenge. In this paper, a freestanding NRR electrocatalyst, BiFeO/FCC, has been developed by in situ growth of bismuth ferrite (Bi25FeO40) on functionalized carbon cloth (FCC), which exhibits high NRR activity with a maximum NH3 yield of 3.88 μg h−1 cm−2 (at −0.40 V vs. reversible hydrogen electrode [RHE]) and a Faradaic efficiency of 12.71% (at −0.45 V vs. RHE) in 0.1 M Na2SO4. The synergistic effect of the abundant exposed bismuth and iron dual active sites confined in the lattice, the binder‐free nature of the electrode and the excellent conductivity of the carbon substrate enable the easy adsorption/activation of N2 and accelerate the electron transfer simultaneously, thus boosting its NRR performance. This work is significant to design low‐cost, and high‐efficient NRR catalysts for large‐scale electrocatalytic NH3 synthesis.

High-Capacity Metal Oxide Electrodes for Lithium-Ion Batteries

It is of paramount importance to develop rechargeable lithium-ion batteries (LIBs) with higher energy to meet the demands of emerging energy storage applications. Currently, LIBs use LiCoO2 as the cathode and graphite as the anode, which shows moderate capacity of ~140 mAh g-1 and ~350 mAh g-1, respectively. As a result, the energy density is limited to 120-160 Wh kg-1. In this context, we have investigated a layered-spinel material (Li2MnO3, LiMn2O4, LiNi2/3Mn1/6Co1/6O2, NMC 811,LiFePO4) as a high-capacity cathode. This cathode exhibits a theoretical capacity of ~ 250 mAh g-1, and in our preliminary work, we demonstrated a high capacity of ~ 250 mAh g-1. We also find that this cathode shows high voltage of 4.5 V and stable cycling over 50 cycles. On the anode side, we investigated BiFeO3(BFO) as a potential high-capacity anode, which delivers a high capacity of ~750 mAh g-1, double the capacity of graphite. In the following research, we will explore the possibility of assembling Li-ion full cells using these two materials in order to demonstrate high energy density.The Li-ion storage mechanism in these two materials will also be thoroughly investigated by electrochemical and physical characterizations, such as electrochemical impedance spectroscopy (EIS), ex-situ XRD, and X-ray photoelectron spectroscopy.

Enhanced photovoltaic and sunlight-driven photocatalysis for water purification study of rare-earth and transition-element-doped bismuth ferrites

Enhanced photovoltaic and sunlight-driven photocatalysis for water purification study of rare-earth and transition-element-doped bismuth ferrites