Structure Of BiFeO3 Research Articles

Study on curie temperature mechanism and electrical properties of BiFeO3-doped (Ba,Ca) (Ti,Sn)O3 ceramics

In this study, we investigated the phase structure, Curie temperature, dielectric properties, piezoelectricity, and energy-storage properties of BiFeO3 (BFO)-modified (Ba0.95Ca0.05) (Ti0.89Sn0.11)O3 (BCTSO) ceramics using both experimental and theoretical methods. The results indicated that the lattice distortion and chaotic distribution of the local charge increased with the BFO content, resulting in a phase transition and transformation from a ferroelectric to a relaxing ferroelectric. First-principles calculations revealed that the Curie temperature decreased with increasing BFO content, primarily because of an increase in the ground state energy. The variation in the permittivity of the BCTSO-xBFO ceramics with temperature and frequency is affected by the phase structure and Maxwell-Wagner interface polarisation, respectively. The electrical modulus measurements indicated that BCTSO-xBFO exhibited non-Debye-type dielectric relaxation for x = 0.0, 0.1, and 0.5 %, whereas BCTSO-xBFO showed Debye-type dielectric relaxation for x = 0.9%.

Systematic investigation on the rational design and optimization of bi-based metal oxide semiconductors in photocatalytic applications

To address the global energy shortage and mitigate greenhouse gas emissions on a massive scale, it is critical to explore novel and efficient photocatalysts for the utilization of renewable resources. Bi-based metal oxide (Bi x MO y ) semiconductors composed of bismuth, transition metal, and oxygen atoms have demonstrated improved photocatalytic activity and product selectivity. The vast number of element combinations available for Bi x MO y materials provides a huge compositional space for the rational design and isolation of promising photocatalysts for specific applications. In this study, we have systematically investigated the electronic and optical properties over Bi2O3 and a series of selected Bi x MO y group materials (BiVO4, BiFeO3, BiCoO3, and BiCrO3) by calculating band structure, basic optical property features, mobility and separation of charge carriers. It is clearly noted that the band gap and band edge position of the Bi x MO y group materials can be tuned in a wide range in comparison to Bi2O3. Similarly, the light response of Bi x MO y also can be broadened from the ultraviolet to the visible light region by adjusting the selection of transition metals. Additionally, the analysis of the effective mass of charge carriers of these materials further confirms their possibility in photocatalytic reaction applications because of the appropriate separation efficiency and mobility of carriers. A selection of experimental investigations on the crystal structure, composition, and optical properties of Bi2O3, BiVO4, and BiFeO3 as well as their catalytic performance in the degradation of methylene blue over was also conducted, which agree well with the theoretical predictions.

Boosting the pseudocapacitance of BiFeO3 by Zn doping for flexible battery-supercapacitor hybrid devices

Perovskite BiFeO3 (BFO) as a type of battery-type electrode materials, usually suffers from poor electrolyte ion transport in the BFO crystal. We propose a novel strategy of Zn doping to improve the ion transport and boost the faradaic pseudocapacitance of BFO for flexible battery-supercapacitor hybrid (BSH) devices. The Zn-doped BFO (Z-BFO-1) with the low Zn doping content, can maintain the crystal structure of BFO and the uniform distributions of elements. The oxygen vacancy content can be increased from BFO to Z-BFO-1, reflecting the influence of the Zn doping on the crystal structure of BFO. The Z-BFO-1 electrode with the stable crystal structure in the charge/discharge process, can provide the highest specific capacitance (223 F g−1 at 0.2 A/g) and the largest Li+ diffusion coefficient (2.386 × 10−11 cm2 s−1) among these BFO-based electrodes with different Zn doping contents. The first-principles calculations reveal that the Zn doping in BFO can significantly enhance the built-in electric fields and greatly lower the Li+ migration energy barriers (from 2.08 eV to 1.43 eV). This flexible MnO2//Z-BFO-1 BSH device with the high energy density (37.5 Wh kg−1 at 0.23 kW kg−1), opens up a new avenue for developing high-performance electrochemical energy storage devices.

Switching the spin cycloid in BiFeO3 with an electric field

Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements. Using nitrogen vacancy-based diamond magnetometry, we observe the magnetic spin cycloid structure of BiFeO3 in real space. This structure is magnetoelectrically coupled through symmetry to the ferroelectric polarization and this relationship is maintained through electric field switching. Through a combination of in-plane and out-of-plane electrical switching, coupled with ab initio studies, we have discovered that the epitaxy from the substrate imposes a magnetoelastic anisotropy on the spin cycloid, which establishes preferred cycloid propagation directions. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the spin spiral propagation vector to changes to specific switching events.

Intermediate bands and p-orbital tuning of the band structure of BiFeO3 for photovoltaic application.

BiFeO3 is a lead-free inorganic ferroelectric material that holds promise for photovoltaic applications. However, its larger band gap poses a challenge for efficient sunlight absorption, limiting its efficiency in such applications. In this work, nitrogen, which has lower electronegativity compared to oxygen, was selected to tune the band gap of BiFeO3. It was discovered that the band gap of BiFeO3-xNx (x = 0.125, 0.25, 0.375, and 0.5) was reduced from the original value of 3.1 eV for the parent phase to 1.45-1.77 eV, which originated from the intermediate bands caused by the stronger interaction between Fe 3d and N 2p and the valence band maximum shifted towards higher energy levels caused by the introduction of N 2p. In particular, the band gaps of 1.45 and 1.49 eV for BiFeO2.75N0.25 and BiFeO2.625N0.375, respectively, were closer to the optimal band gap of approximately 1.4 eV for photovoltaic materials. Accompanied with the reduction in the band gap, the optical absorption coefficient of N-substituted BiFeO3 in the visible range was evidently increased. Noticeably, N-substituted BiFeO3 showed good ferroelectricity with a decreased band gap and increased optical absorption. The presented results thus demonstrate that N substitution is a promising way to improve the ferroelectric photovoltaic properties of BiFeO3.

CO2‐Induced Strong Room‐Temperature Ferromagnetism in BiFeO3

AbstractWith humongous demand for data storage and processing, two‐dimensional (2D) ferromagnetic‐based materials, is emerged as the next‐generation nanoelectronic devices due to their low power consumption and optimal memory and processing capabilities. BiFeO3 as a single‐phase multiferromagnetic material is expected to find potential applications in electromagnetic devices. Herein, 2D room‐temperature ferromagnetic BiFeO3 is obtained with the help of supercritical carbon dioxide (SC CO2). The rhombic phase of BiFeO3 is converted to cubic with the creation of Ov and Fe2+ defects over the SC CO2 treatment, leading to significant ferromagnetic enhancement. More importantly, it is found that SC CO2 can destroy the cycloidal spin structure of BiFeO3 leading to an increase in the Fe─O─Fe bond angle, which generates stronger superexchange interactions. Ultimately, the saturation magnetization strength of BiFeO3 is increased by nearly 23 times. A new strategy is provided for ferromagnetic induction in 2D materials, which is favorable for promoting their practical applications on device architectures in the future.

Dielectric, Magnetic and Surface Analytical Study of Dy and Tb Doped (Bi, Pb)(Fe,Ti)O3 Multiferroic Ceramics

Polycrystalline samples of Bi0.8A0.1Pb0.1Fe0.9Ti0.1O3(where A = Dy and Tb) ceramics have been prepared through high temperature sintering technique. X-ray diffraction analysis showed that the ceramics possess perovskite phase with hexagonal crystal symmetry. Dielectric and electrical properties indicate that the Curie temperature shifted to higher temperature with Dy doping. AC conductivity of the sample increases with increase in temperature which confirms the negative temperature coefficient of resistance (NTCR) behaviour of material. Substitution of Dy and Tb ions at A-site suppress the spiral spin structure of BiFeO3 which is further responsible for the appearance of weak ferromagnetism atroom-temperature.Induced destruction of the spin cycloid due to the Dy and Tb substitution, these multiferroic properties are attributed because of the enhanced magneto-electric interaction.

Phase structure, domain structure, thermal stability, and high-temperature piezoelectric response of BiFeO3–BaTiO3 lead-free piezoelectric ceramics

High-temperature lead-free piezoceramics with a large piezoelectric constant d33 and a high depolarization temperature Td have long been a target of ferroelectric researchers. In this work, (1-x)BiFeO3-xBaTiO3 ceramics with MnO2 and Li2CO3 additives (BF-xBT) were fabricated with traditional ceramic preparation technology. The best piezoelectric ferroelectric properties and thermal stability d33 = 185 pC/N, Pr = 33.152 μC/cm2, Tc = 470 °C, and Td = 460 °C were obtained for x = 0.32. The tetragonal (T) phase content of BF-xBT ceramics increases gradually with an increase of BT content, and the temperature stability improves. In particular, an in-situ d33 test indicates that BF-xBT ceramics have large piezoceramics coefficients with d33 = 450.5 pC/N at a temperature of T = 334 °C. Piezo force microscopy and transmission electron microscopy tests show that nanodomains and polar nanoregions play a key role in the improvement of piezoelectric response. BF-xBT ceramics appear to be the most promising candidates to replace PZT ceramics in high-temperature applications.

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.

Simultaneous existence of magnetic and ferroelectric orders in bi-phase composites for multiferroic applications

Multiferroic materials has brought evolutionary impact in multifunctional devices that are exclusively based on magnetoelectric coupling. In this work, a bi-phasic composite series of the form; (1–x)[Bi0.8La0.2FeO3] + x[Zn0.5Co0.5Fe2O4] was prepared using sol–gel auto–combustion. The X-ray diffraction analysis confirmed the rhombohedrally distorted cubic structure of BiFeO3 and normal spinel cubic structure of Zn0.5Co0.5Fe2O4 having R3c and Fd-3 m space group symmetry, respectively. A reduction in average crystallite size was observed by gradually enhancing the substituent spinel contents (x). Energy dispersive X-ray confirmed the presence of all the constituent elements in accordance with stoichiometrically calculated values. Mostly the particles having spherical shapes were observed via micro-graphical analysis. At x = 0.2, the composite sample showed the highest value of recoverable energy density as 7.2 × 10-2 mJ/cm3 with the highest value of % efficiency ∼ 88.83 %. A clear enhancement in saturation magnetization was observed from 0.16 to 19.87 emu/g. The remanent magnetization also increased from 0.018 to 6.363 emu/g by enhancing the spinel phase contents. Furthermore, coercivity also increased significantly from 672.98 Oe to 841.89 Oe in the composite samples. The highest squareness ratio Mr:Ms was observed at x = 0.3. These distinctive properties of the nanocomposites lead toward potential applications in multiferroic and spintronic devices.

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.

Pressure-Induced Phase Diagram and Electronic Structure Evolves during the Insulator-Metal Transition of Bulk BiFeO3.

BiFeO3 is the most widely known multiferroic at room temperature, possessing both ferroelectricity and antiferromagnetism. It has high Curie temperature and Néel temperature, i.e., 1103 and 643 K, respectively. Despite these unique properties, the pressure-induced phase diagram of bulk BiFeO3 has remained controversial. Based on the ab initio evolutionary algorithm, we systematically searched for the potential stable structures of bulk BiFeO3 at 0-50 GPa. It is identified that there are five pressure-induced phase transition sequences R3c-G-AFM →(5GPa) C2/m-G-AFM →(15GPa) Pnma-G-AFM →(24GPa) Pnma-FM →(35GPa) Imma-FM →(45GPa) Cmcm-FM, which provided a comprehensive pressure-induced phase diagram. As the pressure increases, we discovered an interesting phenomenon: a pressure-induced magnetic sequence transition, i.e., BiFeO3 transitions from an antiferromagnetic to a ferromagnetic sequence. Concurrently, the electronic structure evolves during the insulator-metal transition, influenced not only by the pressure but also by the phase transition. Our research has elucidated the long-standing question of the phase transition sequence of the BiFeO3 system under pressure and provided theoretical support for the insulator-metal transition.

Optical and dielectric properties of ultra-fine Mn doped BiFeO3 nanoparticles

Mn doped and pure BiFeO3 (BFO) with formula BiFe1-xMnxO3 (0≤x≤0.08) were prepared by hydrothermal process. The effects of doping on the microstructure and optical properties have been investigated using X-ray diffraction and both Raman and reflectance diffuse spectroscopies. XRD study revealed that pure and 2 and 4% doped samples present only the rhombohedral symmetry (R3c) typical structure of BFO while 6 and 8% doped samples contain also a cubic (I23) structure that can be attributed to Bi25MnO40 phase. Results showed a variation of structure parameters indicating that Mn can successfully substitute Fe until 4%. Raman spectroscopy revealed a structure distortion caused by the Mn insertion in oxygen octahedra. Temperature depending Raman study confirmed the stability of samples in the range of temperature measurement (from 300 to 800k) and marked the presence of the Neel magnetic transition around the expected TN value. Compared with pure BiFeO3, Mn doped samples present remarkable changes in band structure as shown in plotted Kubelka-Munk function which fit well with the obtained structure results. Direct optical bandgap determined from Tauc plot showed an important decrease in value, which is interesting for photoinduction applications. Dielectric analysis reveals an increase of the dielectric constant and the AC conductivity after Mn doping which can be related to the replacement of Fe3+ by Mn2+ that could enlarge the density of vacancies in the material.

Phase structure and electrical properties of BiFeO3–BaTiO3 ceramics near the morphotropic phase boundary

As a promising lead-free high-temperature piezoelectric material, BiFeO3–BaTiO3 (BF-BT) is still under debate on its crystal structure, especially for the compositions in the morphotropic phase boundary (MPB). Herein, the crystal structure of (1-x)BF-xBT ceramics near the MPB with x = 0.20–0.33 was analyzed by X-ray diffraction and Raman spectroscopy. With the addition of BT, the phase transition from distorted rhombohedral to pseudo-cubic structure was determined by Rietveld refinement. Raman analysis showed the weakening interactions between the A-site cations and BO6 octahedron, as well as the degenerated distortions of BO6 octahedron. Intriguingly, the results of X-ray photoelectron spectroscopy suggested the inhibition of Fe3+ reduction and decrease in oxygen vacancy concentration by the incorporation of BT. In terms of the electrical properties, the significant decline in Curie temperature, improvement in permittivity, and reduction in high-temperature dielectric loss can be observed with the increase of BT content. The increased remnant polarization, enhanced dielectric response and decreased coercive field were helpful for the piezoelectric performance. The maximum room-temperature piezoelectric coefficient of ∼160 pC/N and high-temperature piezoelectric coefficient of ∼324 pC/N were acquired in the x = 0.30 ceramics. This work provides a clear scope for further research on the structural transformation and high-temperature piezoelectric applications of BF-BT system.

Coercive field modified via partial ion substitution, mechanical load and charge injection in (Ba, Ta, Cr) doped BiFeO3 films

Changes in the coercive field of ferroelectric materials translate into variations in the operating power consumption of ferroelectric devices. Here, we have used partial ion substitution to reduce the coercive field in BiFeO3 films deposited by the pulsed laser technique. We have also used mechanical loads without interruption during switching events at the nanoscale to follow the changes in the coercive field. Furthermore, we have analyzed the dependence of the coercive field concerning the injected charges during the writing process. The partial ion substitution of Ba, Ta, and Cr in the BiFeO3 structure causes a reduction of ∼50% in the coercive field due to a weakening in the Asites-O bonds. The mechanical load experiments show that linearly increasing mechanical loading from ∼50 nN to ∼600 nN tends to increase the signal amplitude of the piezoresponse and move the coercive field locations. The linear unloading reduces the amplitude and returns the coercive field to values close to before the force experiment, pointing out a reversible process. Such behavior can be explained by considering that the piezoelectric response is supported and enhanced by the electric field created by the flexoelectric effect during the mechanical loading process due to the small tip radius. Finally, the application of negative (positive) voltage during the writing process caused the loops to shift to the left (right), changing the locations of the coercive field.

Enhanced Cyclic Stability of Cobalt Doped Bi25FeO40/BiFeO3 as an Electrode Material for a Super Long Life Symmetric Supercapacitor Device

BiFeO3/Bi25FeO40 and cobalt doped Bi25FeO40/BiFeO3 are synthesized by a cost-efficient hydrothermal technique. Cobalt is doped at four different concentrations of 1.5, 2.5, 3.5, and 4.5 mmol in a bismuth ferrite composite (BFCO1, BFCO2, BFCO3, and BFCO4). The capacitive behavior of BFCO3 is significantly higher than those of BFO, BFCO1, BFCO2, and BFCO4 based on their structure, morphology, and electrochemical properties. XRD confirmed the formation of a rhombohedral structure of BiFeO3 and cubic crystal structure of Bi25FeO40 and cobalt doped Bi25FeO40/BiFeO3 composites. Raman modes confirm the presence of cobalt doped Bi25FeO40/BiFeO3 in BFCO3. Microsized particles of BFCO1 were broken upon increasing the concentration of cobalt ion in BFCO2, BFCO3, and BFCO4. In BFCO3, the length of the needle is 0.45 μm and breadth is 0.06 μm, which spread over the spherical-shaped particles with an average size of 0.43 μm. The surface area and average pore diameter of BFCO3 are 60.25 m2/g and 3.38 nm, which are relatively higher than the surface area and average pore diameter of BFO, BFCO1, BFCO2, and BFCO4. The capacitive behavior of BFCO3 shows a significantly higher specific capacitance of 605.16 F g–1 at a current density of 1 A g–1 under 3 M KOH as electrolyte in a three-electrode configuration. The symmetric device of BFCO3 exhibits higher specific capacitance of 176.87 F g–1, specific energy of 35.36 Wh kg–1, and specific power of 1199.43 W kg–1 at a current density of 0.5 A g–1 with super long cyclic stability of about 87% capacity retention, and the coulombic efficiency is about 96% even after 10,000 cycles.

Low-cost flame synthesized La2/3Cu3Ti4O12 electro-ceramic and extensive investigation on electrical, impedance, modulus, and optical properties

An environmentally-friendly synthesis route and low-cost starting materials are more appropriate for the production of ceramic materials at the industry level. With this concern we prepared the La2/3Cu3Ti4O12(LCTO), which is isostructural of CaCu3Ti4O12 (CCTO), using the low-cost TiO2 instead of a high-cost of titanium source (titanium isopropoxide or titanium chloride) using a low-cost wet-chemical route. Although, there are lots of synthetic methods reported for LCTO fabrication in terms of duration, cheap reagents, energy consumption, feasibility, etc. The present method is far better than the others. The prepared ceramic samples were sintered at 1050 °C/12 h and studied their structural, morphology and impedance, and modulus studies for further confirmation. The prepared LCTO ceramic shows the pure phase with the cubic type of morphology. The homogenous distribution of all the elements was observed through dispersive X-ray analysis. X-ray photoelectron spectroscopy studies revels that La is in +3 oxidation state, Cu is in a +2 oxidation state, and Ti is multiple (+3 and + 4) oxidation state. The LCTO ceramic displayed the very high dielectric constant (∼3852) and dielectric loss (0.322), at 1 kHz and at room temperature. Calculated the activation energy using the impedance and modulus data and it shows the superior to that of CCTO ceramic synthesized by the same method. The prepared samples exhibited Debye-type relaxation, which is evoked from the impedance and modulus studies. The calculated optical energy bandgap of LCTO (2.06 eV) is found to be lesser than that of the well-known structure of perovskites (BaTiO3 (3.28 eV), PbTiO3 (3.18 eV), LiNbO3 (3.78 eV) and BiFeO3 (2.67 eV) as well as structure of spinel CoCr2O4 (3.10 eV) and LuFe2O4 (2.18 eV)) materials.

Correlation between the unit cell parameters and electronic transitions in Bi1-xEuxFeO3 thin films

Among AFeO3 (A being divalent or trivalent cation) perovskites, BiFeO3 (BFO) exhibits unique as well as complex electronic structure. In the present study local structure of BFO have been manipulated systematically and correlation with the electronic structure has been presented in detail. An electronic energy-level diagram of polycrystalline Bi1-xEuxFeO3 (0 ≤ x ≤ 0.225) has been presented. Using detailed quantitative structural analysis, diffuse reflectance spectrum and the Kubelka-Munk model, the effect of local structural modification on the electronic structure has been investigated. Systematic structural modification has been achieved by Eu3+ substitution which affects bond length, bond angle, and octahedral rotation, consequently, drives the system towards a higher symmetry configuration. Changes in the multiple electronic transitions in pure BFO thin films as a function of Eu3+ substitution have been investigated in detail. An additional change is the emergence of the 4f levels of the rare earth substituent in the valence and conduction bands, Charge-transfer, and doubly degenerated d-d transitions (6A1g→4T2g and 6A1g→4T1g) have been traced as a function of local changes at the unit cell level. In centrosymmetric configuration, 6A1g→4T1g electronic transition is found to be forbidden by the Laporte Rule.

Synthesis and characterization of bismuth ferrite particles using a nano-agitator bead mill

Bismuth ferrite (BiFeO3) nanocomposites were synthesized using a novel nano-agitator bead milling method followed by calcination. Bismuth oxide and iron oxide nanoparticles were mixed in a stoichiometric ratio and milled for 3 h and calcined at 650 °C in air. X-ray diffraction with Rietveld refinement, scanning electron microscopy, and transmission electron microscopy techniques were used to elucidate the structure of BiFeO3. The particle diameter was found to be ∼17 nm. Magnetic and electrical measurements were performed, and these results were compared with those of similar methods. Mostly, BiFeO3 was obtained with minor secondary phase formation. The resulting powder was weakly ferromagnetic with a remnant magnetization of 0.078 emu/g. This can be attributed to residual strain and defects introduced during the milling process. Electrical testing revealed a high leakage current density that is typical of undoped bismuth ferrite.

Investigation on structural, magnetic and optical properties of Sm–Co Co-substituted BiFeO3 samples

Abstract Sol–gel derived Sm–Co co-substituted BiFeO3 ceramics (Bi1–x SmFe1–x Co x O3 with x = 0.0, 0.01, 0.02 and 0.03; named as BFO, BSFCO-1, BSFCO-2 and BSFCO-3, respectively) were investigated for structural, vibrational, magnetic and optical properties. Distorted perovskite rhombohedral structure with R3c crystal symmetry has been established in X-ray diffraction (XRD) patterns analysis by Rietveld refinement and detailed structural parameters like lattice constants, unit cell volume, bond angles, bond length etc. have been evaluated. Raman spectra further confirmed typical rhombohedral structure of BiFeO3 by exhibiting 13 clear Raman active phonon (9E + 4A) modes along with second order modes in the wave number range 50–1500 cm−1. Fourier Transform Infrared (FTIR) spectra showed the presence of Fe–O and Bi–O bands and the calculated Fe–O bond length was in good agreement with that obtained from Rietveld analysis. Room temperature magnetization versus magnetic field (M–H) measurement using Vibrating Sample Magnetometer (VSM) showed enhancement of ferromagnetic ordering parameters with increasing Sm–Co content in BiFeO3 samples. The maximum magnetization values increased from 0.237 emu g−1 for BFO sample to 1.167 emu g−1 for BSFCO-3 sample along with increase in remnant magnetization values. The optical property of Bi1–x SmFe1–x Co x O3 samples was investigated by estimating the energy band gap using UV–Visible spectroscopy. The calculated values of energy band gap were varied in the range 2.46 eV–1.81 eV indicating tuning of energy band gap with Sm–Co co-substitution in BiFeO3 sample.