Structure Of BiFeO3 Research Articles

Determination of rhombohedral structure of BiFeO3 single-domain-like films grown on SrTiO3 and LaAlO3 substrates by X-ray diffraction using

The crystal structure of bismuth ferrite (BiFeO3; BFO) epitaxial films was analyzed by X-ray diffraction (XRD) using a two-dimensional detector. The diffraction spots hex (hexagonal notation was used for the rhombohedral structure in this study) specific to the rhombohedral structure (space group: R3c), which clearly separated from the diffractions in other crystal symmetries of BFO, was used for determining the crystal symmetry. The BFO films on the SrTiO3 substrates were unambiguously identified as R3c with the hex diffraction spot, whereas highly strained BFO films (space group: Cm) on the LaAlO3 substrates did not show the diffraction spot. The structure of a single-domain-like sample with R3c could not be determined using variants, i.e., degrees of freedom for crystal orientation, whereas the Bragg’s diffraction of hex can be used to unambiguously distinguish R3c from other space groups. It was proposed that electron diffraction complemented by nondestructive and high-resolution XRD is highly effective to obtain wide-area reciprocal space information for identifying low-symmetric-complex materials such as BFO.

Co-substitution induced structural transition with enhanced magnetic and electrical properties of multiferroic BiFeO3 nanoparticles

Polycrystalline Bi1−xTbxFe1−xCoxO3 (for x = 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by tartaric acid assisted sol–gel route. The quantitative crystallographic phase analysis of XRD pattern demonstrates the subsequent structural phase transition from rhombohedral (R3c) to cubic (Pm $$\bar {3}$$ m) with the intermediate orthogonal (Pbnm) and orthogonal (Pnma) phase with the gradual increase in concentration of co-substituents. Raman spectroscopic analysis emphasizes that all the co-substituted samples has undergone structural phase transitions which are in good agreement with the results of Rietveld analysis. X-ray photoelectron spectroscopy (XPS) have confirmed that Fe exists predominantly in +3 state in the co-substituted sample. The enhancement in the room temperature magnetic behavior of the sample can be attributed to the co-substitution induced suppression of spatially modulated spiral spin structure of BiFeO3. All the samples exhibit dielectric anomaly at the vicinity of Neel temperature (TN) signifies the change in magnetic ordering. Moreover, all the co-substituted samples have been witnessed with reduced leakage current and improved ferroelectric behaviour, which is the desirable characteristics for multifunctional device applications of multiferroics.

Effect of Modification on the Structure, Microstructure, and Dielectric and Electrophysical Characteristics of (1 − x)BiFeO3−xBaTiO3 Binary Solid Solutions

The effect modification by Mn2O3(III) manganese oxide has on the structure, microstructure, and dielectric and piezoelectric characteristics of the ceramics of (Bi0.95 − xPb0.05 + x)(Fe0.95 − x/2Ti0.05Nbx/2)O3 binary solid solutions (x = 0.25, 0.30, 0.35) is studied. The formation of crystal structure and the dielectric and piezoelectric parameters of ceramics are investigated within wide ranges of temperature and frequency.

Improved magnetization and reduced leakage current in Sm and Sc co-substituted BiFeO3

BiFeO3 (BFO) and Bi0.85Sm0.15Fe0.90Sc0.10O3 (BSFSO) ceramics were synthesized by conventional solid state route. X-ray diffraction measurements revealed that an orthorhombic Pnma structure evolved with a phase fraction of 84% in the rhombohedral R3c structure of BFO upon the substitution of Sm and Sc. The changes in the intensity and the frequency of Raman modes also corroborated the structural transformation in the BSFSO compound. A decrease in grain size, reduction in porosity, and improved density were observed in the BSFSO compound. An enhanced remanent magnetization of 0.2 emu/g and coercive field of 6.2 kOe were observed, which were attributed to the structural change as well as the destruction of the spin structure with the substitution. Impedance and leakage current measurements revealed that the insulating character of BFO was improved with the substitution of Sm and Sc in BFO and was explained based on the bond enthalpy concept. The enhanced magnetic properties along with the improved insulating character of BSFSO compound will be suitable for device applications.

Structural transition and its effect on magnetoelectric coupling in the BiFe1−xMnxO3 ceramics prepared by sol–gel method

Significant perturbation on the local magnetic structure and related behavior in BiFeO3 is achieved through a substitution of Fe by Mn. The BiFe1−xMnxO3 ceramics were synthesized by sol–gel method and self-sustaining combustion. The crystal structure of BiFe1−xMnxO3 (0 ≤ x ≤ 0.3) changes from rhombohedral R3c to orthorhombic Pbnm forming a biphasic region at 0.05 ≤ x ≤ 0.15. It is found that the phase fraction change can effectively regulate the macroscopic magnetization and magnetoelectric coupling. The amount of the R3c phase reduces significantly with the Mn content increasing. The ceramic consisting of two phases with almost equal fractions shows a remnant magnetization and magnetoelectric coupling coefficient of 0.40 emu/g and 7.65 mV/(cm·Oe), respectively.

Photocatalytic activity and magnetic enhancements by addition of lanthanum into the BiFeO3 structure and the effect of synthesis method

In this paper, the photocatalytic activity, as well as the magnetic enhancement of multiferroics BiFeO3 (BFO) and Bi0.8La0.2FeO3 (BLFO) nanocrystals with two different morphologies, synthesized by two different sol–gel and hydrothermal (HT) methods, have been studied. All the obtained samples were characterized using X-ray diffractometer, Fourier transform infrared spectroscopy, transmission electron microscopy, UV–Vis spectroscopy and vibrating sample magnetometer. Differential thermal analysis measurements were probed ferroelectric- paraelectric first-order phase transition (TC) for all samples. Addition of lanthanum decreases the electric phase transition. For photocatalyst application of bismuth ferrite, adsorption potential of nanoparticles for methylene blue (MB) organic dye was evaluated. The doping of La in the BFO structure enhanced the photocatalytic activity and about 71% degradation of MB dye was obtained under visible irradiation. The magnetic properties of BLFO nanoparticles improve compared to the undoped BiFeO3 nanoparticles. The non-saturation at high applied magnetic field for as-prepared samples by HT is related to the size and shape of products. This work not only presents an effect of 20 mol% lanthanum substitution into the bismuth ferrite structure on the physical properties of BFO, but also compares the synthesis method and its influence on the photocatalytic activity and multiferroics properties of all nanopowders.

Correlation of sintering temperature with structural and multiferroic properties of un-doped and cobalt doped bismuth ferrite

The crystal structure and physical properties of BiFeO3 and BiFe0.95Co0.05O3 sintered at various sintering temperature were studied using x-ray diffraction, scanning electron microscopy (SEM), electric and magnetic measurements. All the samples crystallize in a distorted perovskite structure with space group R3c and show minor impurity phase. An influence of various structural parameters and electronic states over physical properties of all the compounds were investigated. Partial covalency of the Bi–O bonds was confirmed using electron density calculation. Density functional theory (DFT) calculation has supported the validity of the experimental results. Moreover, microstructural investigation using the SEM shows that Co substitution in BiFeO3 increases the grain growth and increases the average grain size when sintered at 800 °C. P–E loop confirmed the ferroelectric behavior of synthesized compounds. The remnant magnetization Mr of BiFe0.95Co0.05O3 compound sintered at 850 °C was enhanced significantly, which provides potential applications of the material in information storage.

Photocatalytic activity, optical and ferroelectric properties of Bi0.8Nd0.2FeO3 nanoparticles synthesized by sol-gel and hydrothermal methods

In this study, the effects of synthesis method and dopant neodymium ion on the ferroelectric properties and photocatalytic activity of bismuth ferrite were studied. BiFeO3 (BFO) and Bi0.8Nd0.2FeO3 (BNFO) nanoparticles were prepared through a facile sol-gel combustion (SG) and hydrothermal (HT) methods. The as-prepared products were characterized by X-ray powder diffraction (XRD), Furrier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM) images. Both nanophotocatalysts have similar crystal structures, but the SG products have semi-spherical morphology. On the other hand, HT samples have rod-like morphology. The ferroelectric properties of BNFO nanoparticles were improved compared to the undoped bismuth ferrite. The photocatalytic activity of as-synthesized nanoparticles was also evaluated by the degradation of methyl orange (MO) under visible light irradiation. The SG as-prepared nanoparticles exhibited a higher photocatalytic activity compared to powders obtained by HT method. Also substitution of Nd into the BFO structure increased the photocatalytic activity of bismuth ferrite.

Single BiFeO3 and mixed BiFeO3/Fe2O3/Bi2Fe4O9 ferromagnetic photocatalysts for solar light driven water oxidation and dye pollutants degradation

A simple synthesis route is presented to obtain single BiFeO3 and mixed BiFeO3/Fe2O3/Bi2Fe4O9 photocatalysts. The obtained samples were characterized to analyze their structural, magnetic, optical and physical–chemical properties. The role of additional phases, i.e. Bi2Fe4O9 and Fe2O3 in the BiFeO3 structure, was analyzed by investigating sunlight-driven water oxidation and degradation of different dye pollutants. The achieved results suggest formation of BiFeO3/Fe2O3/Bi2Fe4O9 heterojunction-like interfaces, that induce lower e−/h+ recombination rate, thus enhancing photoactivity than bare BiFeO3. Additionally, BiFeO3/Fe2O3/Bi2Fe4O9 has exclusive feature of being magnetically separated from treated media and its stability was demonstrated for at least 3 cycles of dye degradation.

Effect of Zn and Ti Co-doping on structure and electrical properties of BiFeO3 ceramics

In this paper, the effect of Zn and Ti co-doping on the structure, dielectric, ferroelectric and magnetic properties of BiFeO3 (BFO) ceramics have been studied. Co-doped BFO ceramics with different doping concentrations are prepared by using the sol-gel method. The structure, morphology and electrical properties of co-doped BFO ceramics are studied by using X-ray diffraction (XRD), scanning electron microscopy, impedance analyzer and ferroelectric test analysis system. Furthermore, the vibrating sample magnetometer (VSM) is used to investigate the magnetic properties. The structural transition from rhombohedral to tetragonal-like phase is observed with a high level of co-doping (x = 2.5%). In addition, higher content of Zn and Ti results in enhanced dielectric constant (ε) and reduced dielectric loss (tanδ). The highest remnant polarization of 0.4 μC/cm2 and coercive electric field of 15.5 kV/cm is demonstrated at x = 2.5%. The enhanced dielectric and ferroelectric properties can be attributed to the formation of defect complexes due to the Zn and Ti substitution.

Ferroelectricity and Elasticity of Rhombohedral BiFeO3 Under Uniaxial Stress

We report on first‐principles calculations of electric polarization in multiferroic rhombohedral BiFeO3 under the [111] uniaxial stress, and our results suggest that the polarization varies nearly linearly from 75.5 to 97.1 μC cm−2 within the stress range of 8 to −8 GPa. The change of polarization is mainly due to atomic displacements since the calculated Born effective charges barely change under stress. We also compute the elastic stiffness coefficients and the elastic compliance coefficients, and these results demonstrate that the rhombohedral structure of BiFeO3 remains stable under the uniaxial stress between 8 and −8 GPa. Because in a ferroelectric‐based photovoltaic cell the photocurrent is proportional to the magnitude of electric polarization, it is possible to improve the photovoltaic efficiency of BiFeO3 thin film by applying uniaxial stress.

Remarkable improvement of ferroelectric properties and leakage current in BiFeO3 thin films by nd modification

Ferroelectric and leakage properties are important for ferroelectric applications. Pure and Nd-doped (x=0.05-0.20) BiFeO3 thin films were fabricated by sol-gel method on FTO substrates. The phase structure, surface morphology, leakage current, ferroelectric properties, and optical properties of BiFeO3 - based thin films were investigated. The substitution of Nd3+ ions for the Bi3+ site converts the structure from rhombohedral to coexisting tetragonal and orthorhombic. Nd doping improves the crystallinity of BiFeO3 thin films. The leakage current of Nd-doped BiFeO3 decreases by two to three orders of magnitude compared with that of pure BiFeO3. Among the samples, 15% Nd-doped BiFeO3 exhibits the strongest ferroelectric polarization of 17.96 μC/cm2. Furthermore, the absorption edges of Bi1-x Nd x FeO3 thin films show a slight red-shift after Nd doping.

Thickness-dependent multiferroic behavior of BiFe0.75Cr0.25O3 films over Pt(111)/Ti/SiO2/Si substrate

We present here the experimental results of BiFe0.75Cr0.25O3 (BFCO) thin film deposited by sol–gel spin coating technique directly on Pt(111)/Ti/SiO2/Si substrate at different thicknesses. The crystal structure of BFCO has been investigated using X-ray diffraction which acts as a double perovskite structure with high crystallinity obtained at 400 °C. Further microscopic studies such as scanning electron microscope (SEM) with EDAX, transmission electron microscope (TEM) were also used in identifying the grain size and particle distribution over Pt (111) substrate. Atomic force microscopy (AFM) on the films at a different thickness (− 80 to − 250 nm) reveals that the surface roughness and other amplitude parameters increases with the increase in thickness signifying an increase of grain size with thickness. Increase in grain size and substrate clamping effect between the BFCO film and the substrate induces change in ferroelectric polarization and dielectric properties in relation to thickness effect. Similarly, decrease in magnetization from 9.241 emu/cm3 (− 80 nm) to 5.7791 emu/cm3 (− 250 nm) is attributed to the formation of anti-sites and anti-phase boundaries in the films. In addition, temperature dependence of magnetization reveals ferromagnetic super-exchange interaction of BFCO which is unlike the spin structure of antiferromagnetic BiFeO3.

Effect of Nd Substitution on Properties of Multiferroic Bismuth Ferrite Synthesized by Sol-Gel Auto-combustion Method

In this work, pure and Nd-doped bismuth ferrite nanocrystals with the general formula of Bi1−x Nd x FeO3 (x = 0, 0.05, 0.1, 0.15, 0.2) were synthesized via the sol-gel auto-combustion method at two different calcination temperatures (550 and 650∘C). Phase analysis and investigating structural, thermal, and magnetic properties and measuring the size of nanoparticles have been done by using X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric and differential thermal analysis (TG/DTA), and vibrating sample magnetometry (VSM). For undoped BiFeO3 (BFO), increasing calcination temperature will increase the average size of nanocrystals. On the other hand, the average size of nanoparticles is decreased by increasing the concentration of neodymium in the structure of BFO. By entering neodymium to the structure of bismuth ferrite at the calcination temperature of 550∘C, the ferromagnetic properties decline. However, at 650∘C, ferromagnetic properties are improved which is due to a fall in the number of Fe2+ ions. In this case, by decreasing the Fe2+ ions, remanent and saturation magnetization increase.

Surface modification and enhanced multiferroic behavior of BiFe0.25Cr0.75O3 films with different thickness over Pt(111)/Ti/SiO2/Si substrate

Polycrystalline BiFe0.25Cr0.75O3 thin films have been fabricated via a chemical deposition technique at various thicknesses (60-, 130-, 190-, 240 nm). The effect of Cr substitution on BiFeO3 structures have been briefly discussed by performing X-ray diffraction and SAED pattern. The nature of the films surface at different thicknesses were briefly discussed using scanning electron microscope and transmission electron microscope. Roughness and other amplitude parameters of the film at different thickness are studied through atomic force microscopy. The result indicates that, when changing the thickness of the film, the average bond length gets changed causing difference in electrical and magnetic properties. Electrical and dielectric study reveals thickness dependent property and is deeply understood from space charge, oxygen vacancies and super-exchange interaction. Film at 60 nm shows higher magnetization with 8.5042 emu/cm3 and with a retentivity of 3.852 emu/cm3 than the thick film. Further, the spin-cooling behavior and magnetization below room temperature from 2 to 300 K were analyzed briefly for spintronics applications.

Multiferroic properties of Sr-doped BiFeO3 nanoparticles

The effects of ‘Sr-doping’ and ‘particle size’ on multiferroic properties of BiFeO3 nanoparticles were studied. Structural analysis revealed no influence on the rhombohedral structure of BiFeO3 with Sr-doping in the synthesized nanoparticles. The particle size of Sr-doped BiFeO3 nanoparticles was tailored by varying calcination temperature. The crystallite size got reduced with Sr-doping and also on decreasing the calcination temperature. Lattice strain was observed to enhance with reducing particle size of Sr-doped BiFeO3 nanoparticles. Magnetic measurements confirmed enhancement in magnetization via suppression of spin cycloidal structure with Sr-doping owing to creation of oxygen vacancies, enhanced lattice strain and reduction in particle size. Dielectric analysis revealed deterioration of dielectric constant of BiFeO3 with Sr-doping due to the formation of oxygen vacancies. Further, on reducing particle size of Sr-doped BiFeO3 nanoparticles, both saturation magnetization and dielectric constant values registered increase. Lowering of the magnetic phase transition temperature with particle size of Sr-doped BiFeO3 nanoparticles indicated weakening of magnetic exchange interactions.

The first-principles calculations on trigonal and hexagonal structures of BiFeO3

ABSTRACTThe band structures, density of states and optical properties of trigonal and hexagonal structures of BiFeO3 (BFO) were calculated by density functional theory (DFT) pseudo-potential plane-wave method and generalized gradient approximation (GGA). The calculated band structure of hexagonal exhibits an indirect band-gap with an energy gap of 2.606 eV, which is larger than that of trigonal structure (direct band-gap around 2.401 eV). Ferromagnetism and ionicity of hexagonal structure are better than that of trigonal. From the spectrogram of absorption and conductivity, it is found that the absorption process of BFO includes lattice vibration absorption and intrinsic absorption.

Doping effect on ferromagnetism, ferroelectricity and dielectric constant in sol-gel derived Bi1−xNdxFe1−yCoyO3 nanoceramics

Doping at the post-transition metal site by trivalent rare-earth ions and 3d transition metal site by transition metal ions in perovskite lattice has observed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report large ferromagnetism and enhanced dielectric constant (at ∼100 Hz) in chemically synthesized single phase multiferroic Bi1−xNdxFe1−yCoyO3 (x = 0, 0.10; y = 0, 0.10) nanoparticles (average particles size ∼45 nm). We have also examined the ferroelectric nature of our chemically synthesized samples. The Rietveld refinement of the XRD data reveals the structural symmetry breaking from distorted rhombohedral R3c structure of BiFeO3 to the triclinic P1 structure in Bi0.9Nd0.1Fe0.9Co0.1O3 (BNFCO) without having any iron rich impurity phase. The magnetization in these nanoceramics most likely originates from the coexistence of mixed valence states of Fe ion (Fe2+ and Fe3+). A high room temperature dielectric constant (∼1050) has been observed at 100 Hz of BNFCO sample. The frequency dependent anomalies near Neel temperature of antiferromagnet in temperature variation of dielectric study have been observed for all the doped and co-doped samples exhibiting typical characteristic of relaxor ferroelectrics. A spectacular enhancement of remanent magnetization MR (∼7.2 emu/gm) and noticeably large coercivity HC (∼17.4 kOe) at 5 K have been observed in this BNFCO sample. Such emergence of ferromagnetic ordering indicates the canting of the surface spins at the surface boundaries because of the reduction of particle size in nanodimension. We have also observed P-E hysteresis loops with a remanent polarization of 26 μC/cm2 and coercive field of 5.6 kV/cm of this sample at room temperature. From impedance spectroscopy study the estimated activation energy of 0.41 eV suggests the semiconducting nature of our nanoceramic BNCFO sample.

Brown pigments based on perovskite structure of BiFeO3−δ

Light brown inorganic pigments based on BiFeO3 doped by Sr2+ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi1−x Sr x FeO3−δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO3 is 1046 K, whereas the substitution of 20 mol% of Bi3+ by Sr2+ ions shifted it to 1403 K and powder with composition Bi0.65Sr0.35FeO3−δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi0.85Sr0.15FeO3−δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).

Accuracy and Transferability of Ab Initio Electronic Band Structure Calculations for Doped BiFeO3

BiFeO3 is a multiferroic material and, therefore, highly interesting with respect to future oxide electronics. In order to realize such devices, pn junctions need to be fabricated, which are currently impeded by the lack of successful p-type doping in this material. In order to guide the numerous research efforts in this field, we recently finished a comprehensive computational study, investigating the influence of many dopants onto the electronic structure of BiFeO3. In order to allow for this large scale ab initio study, the computational setup had to be accurate and efficient. Here we discuss the details of this assessment, showing that standard density-functional theory (DFT) yields good structural properties. The obtained electronic structure, however, suffers from well-known shortcomings. By comparing the conventional DFT results for alkali and alkaline-earth metal doping with more accurate hybrid-DFT calculations, we show that, in this case, the problems of standard DFT go beyond a simple systematic error. Conventional DFT shows bad transferability and the more reliable hybrid-DFT has to be chosen for a qualitatively correct prediction of doping induced changes in the electronic structure of BiFeO3.