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In photoelectrochemical (PEC) water splitting, charge separation and collection by the electric field in the photoactive material are the most important factors for improved conversion efficiency. Hence, ferroelectric oxides, in which electrons are the majority carriers, are considered promising photoanode materials because their high built-in potential, provided by their spontaneous polarization, can significantly enhance the separation and drift of photogenerated carriers. In this regard, the PEC properties of BiFeO thin-film photoanodes with different crystallographic orientations and consequent ferroelectric domain structures are investigated. As the crystallographic orientation changes from (001) via (110) to (111), the ferroelastic domains in epitaxial BiFeO thin films become mono-variant and the spontaneous polarization levels increase to 110 μC/cm. Consequently, the photocurrent density at 0 V vs. Ag/AgCl increases approximately 5.3-fold and the onset potential decreases by 0.180 V in the downward polarization state. It is further demonstrated that ferroelectric switching in the (111) BiFeO thin-film photoanode leads to an approximate change of 8,000% in the photocurrent density and a 0.330 V shift in the onset potential. This study strongly suggests that domain-engineered ferroelectric materials can be used as effective charge separation and collection layers for efficient solar water-splitting photoanodes. [ABSTRACT FROM AUTHOR]

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 BiFeO based thin films were investigated. The substitution of Nd ions for the Bi3+ site converts the structure from rhombohedral to coexisting tetragonal and orthorhombic. Nd doping improves the crystallinity of BiFeO thin films. The leakage current of Nd-doped BiFeO decreases by two to three orders of magnitude compared with that of pure BiFeO. Among the samples, 15% Nd-doped BiFeO exhibits the strongest ferroelectric polarization of 17.96 μC/cm. Furthermore, the absorption edges of BiNdFeO thin films show a slight red-shift after Nd doping. [ABSTRACT FROM AUTHOR]

The recent discovery of efficient charge separation in tetragonal–rhombohedral (T‐R) polymorphic phase boundaries (PPBs) in strained BiFeO3 (BFO) films is of great interest, and also raised a question of whether the PPBs could enhance the performance of BFO‐based planar photodetectors. To address it, we prepare BFO films with thickness ranging from 8 to 90 nm on the LaAlO3 substrates, in which the BFO evolves from a pure T phase (without PPBs) to a T‐R mixed phase (with PPBs) due to the strain relaxation. Then, we comparatively investigate the photoconductive properties of these BFO films with the planar device geometry. It is found that the photoconductance first increases and then decreases with increasing film thickness. Particularly, the 50‐nm film containing the pure T phase without any detectable PPBs exhibits the highest photoconductance. This unexpected observation can be understood by analyzing the effects of increasing film thickness and associated phase evolution on the photoconduction‐related parameters. [ABSTRACT FROM AUTHOR]

The pure BiFeO (BFO) and (Nd, Zn)-co-doped BFO nanoparticles were prepared by a sol-gel method. The crystal structure and optical and multiferroic properties of the samples were systematically investigated. Rietveld refinement showed that the samples crystallized in rhombohedral R3c structure. In UV-visible diffuse absorption spectra, an apparent blue shift can be observed after co-doping, which indicates a possible application in photocatalyst and photoconductive devices. Compared with a pure BFO sample, the leakage current density of the x = 0.05 sample decreases about 3 orders of magnitude. The remanent magnetization ( M ) of the x = 0.10 sample reaches 0.105 emu/g while the coercive field ( H ) is as high as 7.0 kOe. The (Nd, Zn) co-doping into BFO nanoparticles has been proved to be an effective way to improve the optical and multiferroic properties. [ABSTRACT FROM AUTHOR]

The co-doped BiDyFeM O (M = Mn, Co) samples were successfully prepared by a solid-state reaction method. At room temperature, the structural, ferromagnetic, and ferroelectric properties of the samples were measured and analyzed. An x-ray diffraction (XRD) experiment shows that co-doping leads to some structure changes. Magnetic hysteresis loops indicate that Dy-Mn and Dy-Co co-doping both can increase the ferromagnetic but the latter is superior to the former caused by the different magnetic arrangement. Furthermore, it is found that Dy-Mn co-doping is better than Dy-Co co-doping on enhancing its ferroelectricity. [ABSTRACT FROM AUTHOR]

Stable catalysts require high catalytic efficiency and repeated consecutive use, low mass loss, and metal leaching. This study investigated BiFeO (BFO) composite with high stability and reusability using a one step microwave-assisted hydrothermal method (MAHS) to decompose bisphenol A (BPA) used as the target contaminant. After six consecutive reaction cycles in microwave-enhanced Fenton-like process (MW-Fenton-like), the removal rate of BPA decreased from 94 to 87.4% with low metal leaching ratio and mass loss. The morphology, crystal, reaction kinetics, and hydroxyl radical (·OH) were used to demonstrate the high stability of BFO-MAHS. The results indicated that the benign stability and reusability of BFO-MAHS probably occurred because (1) the thermal-effect of MW improved heating rate, which led to the rapid formation stable cube structure and (2) MW mechanical vibrations existed in the preparation process, which further enhanced the cube structure. Therefore, MAHS could be used as a green and environmental friendly method to apply in catalysts synthesis, which could immensely shorten preparation time and enhance the catalytic performance with no waste production. [ABSTRACT FROM AUTHOR]

Room-temperature multiferroic (1 − x)BiFeO- x(SrTiO-BiNaTiO) (BFO-ST-BNT) ( x = 0 to 0.5) solid solutions have been prepared by the modified Pechini method, and their structural, ferromagnetic, ferroelectric, and dielectric properties systematically studied. In addition, a gradual phase transformation from rhombohedral to pseudocubic structure was observed between the compositions with x = 0.2 and x = 0.3. Compared with pure BiFeO, significantly enhanced remanent magnetization ( M = 0.11 emu/g) was determined in the sample with x = 0.2 at room temperature. Although the ferroelectric properties exhibited overall enhancement with increasing x, relatively large remanent polarization P (1.14 μC/cm at 300 K) was achieved simultaneously at the optimal composition with x = 0.2. Moreover, we measured an outstanding relative dielectric constant of over 16,700 at frequency of 10 kHz for the sample with x = 0.2, which is attributed to polarization of defect dipoles. This comprehensive enhancement of the ferromagnetic, ferroelectric, and dielectric properties indicates that BFO-ST-BNT ceramics are promising candidates for use in multiferroic applications. [ABSTRACT FROM AUTHOR]

Even though it is a potential visible-light responsive photocatalyst, the application of BiFeO (BFO) is restricted because of the presence of residual impurities in the synthesis process. To alleviate this problem, in this work, BiFeO was synthesized by the sonochemical method and calcined at different temperatures. Morphologies and phases of the samples were evaluated by using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques. UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) was used to analyze the absorption properties. The photocatalytic activities of the samples were evaluated via the photocatalytic degradation of rhodamine-B (RhB) aqueous solution under simulated solar light irradiation. The results revealed that the phase transformation from amorphous to crystalline phase has occurred during heat treatment. The formation of pure BFO occurred only at about 600 °C, indicating the importance of heat treatment during the synthesis process. On the other hand, the decolorization of RhB solution was completed by pure BFO photocatalyst within 1 h of simulated solar light irradiation. [ABSTRACT FROM AUTHOR]

In the present study, the co-precipitation method has been used to grow BiFeO powders, which are pressed into pellets and sintered at 450, 500 and 550 °C for 2 h in a muffle furnace. The crystalline nature is studied by x-ray diffraction (XRD), which depicts multiphase formation. The un-annealed sample shows highest peak belonging to BiFeO, while smaller peaks of BiFeO and Bi(BiFe)O are also evident. With increase in sintering temperature 450 − 550 °C, the major peak belonging to BiFeO decreases and peaks intensities of other phases increase indicating that some phases grow at the expense of others. The surface morphology, as determined by scanning electron microscopy (SEM), reveals grains of varying sizes and shapes. The vibrating sample magnetometer (VSM) is used elucidate the magnetic characteristics, which have been observed to strongly depend upon the sintering temperature. The phase formation behaviours of this material system may be useful to optimize the fabrication conditions for the realization of single-phase BiFeO. [ABSTRACT FROM AUTHOR]

The (1- x)BiFeO- xSrTiO (BFO- xSTO, x = 0, 0.05, 0.10, 0.20, 0.30) solid solution thin films were fabricated by a sol-gel method. The X-ray diffraction patterns showed that a phase transition appeared as the SrTiO modified BiFeO. The structural properties of all the samples were analyzed by Raman spectroscopy. Scanning electron microscope images showed that all thin films have dense and uniform surface morphology. Compared with that of BiFeO thin film, BFO- xSTO enhanced its ferroeletric properties significantly. BFO-0.20STO thin film possessed the lowest leakage current and larger polarization with well-defined ferroelectric hysteresis loop. In order to investigate the optical properties, ellipsometric spectra of BFO- xSTO thin films on Si substrates were measured and the experimental data were fitted by using a model consisting of air/roughness/BFO- xSTO/Si(100). The optical constants and the band gaps of BFO- xSTO thin films were obtained. The optical band gaps linear increase with the increasing of SrTiO content. The results indicate a promising ability for improving the BiFeO ferroelectricity by introducing SrTiO to enable functionality as multiferroic informational storage devices while tuning the BiFeO band gap as a wide band gap photovoltaic material. Graphical Abstract: [ABSTRACT FROM AUTHOR]

BiFeO nanoparticles have been synthesized by hydrothermal method. Ag nanospheres (1 wt%) have been successfully decorated on the surface of BiFeO nanoparticles by photo-deposition method. XPS study confirms the decoration of Ag on the surface of BiFeO. Synthesized nanoparticles have been characterized by studying their morphological, structural, optical and photocatalytic properties. It has been found that the photocatalytic properties of Ag decorated BiFeO nanoparticles to decompose methylene blue in visible light are far better than those of bare BiFeO nanoparticles. The mechanism of enhanced photocatalytic activities of Ag-decorated BiFeO nanoparticles has been disclosed. Graphical Abstract: [ABSTRACT FROM AUTHOR]

We investigate the ferroelectric state of a tetragonal BiFeO thin film grown on a LaAlO (001) substrate using an optical second harmonic generation (SHG) microscope. Whereas the ferroelectric state of this material hosts nanometer-sized domains which again form micrometer-sized domains of four different configurations, we could figure out the characteristic features of each domain from the SHG mapping with various sizes of the probe beam, i.e., from 0.7 to 3.9 μm in its diameter. In particular, we demonstrate that a single micrometer-sized domain contributes to the SHG as a coherent summation of the constituent nanometer-sized domains, and multi-micrometer-sized domains contribute to the SHG as an incoherent summation of each micro-domain. [ABSTRACT FROM AUTHOR]

The present work addresses the influence of Ca doping and (Eu, Ca) co-doping into BiFeO on its corresponding structural, magnetic, and ferroelectric properties. XRD results show that Bi site doped with Ca and Eu could result in a transition of crystal structure. Analysis of magnetic hysteresis data reveals a further enhancement of magnetism in the (Eu, Ca)co-doped samples which is explained by the structural distortions and the magnetically active characteristic of Eu ions. High remnant polarization at room temperature was observed in the BiEuCaFeO samples by measuring the electric hysteresis loops due to Eu doping suppressing the formation of Fe and oxygen vacancies. [ABSTRACT FROM AUTHOR]

Polycrystalline antiferromagnetic BiFeO (BFO) thin films were grown on Si/SiO/Ti/Pt (111) substrates by pulsed laser deposition and then ferromagnetic films CoFe(AlSi) (CFAS) by magnetron sputtering. After fabrication, the films were vacuum-annealed under a 0.1-T magnetic field at different temperatures from 150 to 500 °C. The exchange bias field can be tuned by the annealing temperature for the heterostructures, and the electric domain size can be controlled by the crystal grain size. A large exchange bias of about 5 × 10 T is observed in one of the samples. It can be speculated that the crystal grain sizes are the key element in determining the exchange bias and coercivity of the films annealed at the temperature of higher than Neel temperature ( T ) of BFO. Furthermore, it is possible to extend spin theories from single-crystal BFO system to polycrystalline BFO system. [ABSTRACT FROM AUTHOR]

BiFeO-based multiferroic ceramics if prepared in phase pure form possess wide range of applications based on their charming and switchable polarization, piezoelectric, magnetoelectric and spintronic properties. In this regard, we investigate the influence of Mn substitution at Fe-site in BiFeCuO samples, synthesized by sol-gel-based self-assisted combustion technique. Crystal structure was determined using X-ray diffraction which revealed a rhombohedrally distorted cubic perovskite structure of all the samples. The lattice constant increased, while crystallite size decreased with increased concentration of Mn. A systematic analysis of frequency-dependent dielectric constant, loss factor, tangent loss and impedance has been presented using an impedance analyzer. It is observed that the trend of dielectric constant, loss factor, tangent loss and impedance is decreasing with increasing frequency. It was also observed that electrical properties were mainly influenced by dominance of grain boundaries effect in 20 Hz-20 MHz range. Effect of increased concentration of Mn on frequency-dependent dielectric properties has also been discussed, and it is found that dielectric properties decreased with increasing concentration of Mn mainly attributed to the suppression of oxygen vacancies. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Nanoparticles of BiZrFeCuO ( x = 1 %, 2 %, 3 %, 4 %, 5 %) were prepared by sol-gel method. The influences of Zr dopant on the characteristics of polycrystalline BiFeO (BFO) have been studied. X-ray diffraction study confirms the formation of nanocrystalline rhombohedral phase without distortion. The average crystallite size is found to vary from 31 to 60 nm. All the samples exhibited well-saturated ferromagnetic hysteresis. A notable increase in the saturation magnetization (M) and remnant magnetization (M) has been observed with increase in dopant percentage. Improved ferromagnetic and magnetoelectric behavior of BFO nanoparticles is found to be the result of doping. The Zr and Cu doping has improved the ferroelectric properties of the BFO. The variation in the surface morphology is also attributed to Zr doping of BiFeO. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The sequence of phases appearance during the formation of BiNdFeO solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO or NdFeO) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics BiNdFeO as the final product, due to the prevalence of various interphase contacts in the starting reaction zone. [ABSTRACT FROM AUTHOR]

Partial substitution of Tb at Bi site results in change of structure from rhombohedral to orthorhombic. Transmission electron micrograph shows the variation of particle size from 15-75 nm. Tb doping enhances the magnetic as well as electric properties of BiFeO. Electric and magnetic behaviours of BiTbFeO nanoparticles of different particle sizes reveal their enhancement as the particle size reduces. The signature of magnetoelectric coupling was marked by magnetic field dependence of polarization. The magnetoelectric coupling enhances with magnetic field due to magnetostriction effect. The calculated linear magnetoelectric coefficient registers a rise roughly by an order of one (10 to 10) on reducing particle size, which is precisely due to higher strain and increased suppression of spin spiral structure. [ABSTRACT FROM AUTHOR]

The high-concentration precursor solution of BiLaFeO (BLFO) was fabricated and stored under the different temperatures (40, 20, 0 °C). After 10 days, the solution at the temperature of 40 °C generated both bismuth acetate precipitation and nitrogen dioxide gas and at the temperature of 20 °C generated nitrogen dioxide gas, while the solution still maintains stability and transparency at the temperature of 0 °C. These results show that low temperature is an important way to improve the stability of high-concentration precursor solution in sol-gel method. Furthermore, the stability precursor solution is adopted to prepare BLFO thick film on indium tin oxide/glass substrate by spin coating combined with sequential layer annealing. The film exhibits a perovskite structure without impurity phase; especially, a comparatively high remanent polarization ( P ) of 42.85 μC/cm can be obtained, which may be related to lanthanum doping, preferred (110) orientation and relatively compact microstructure. Graphical Abstract: XRD patterns and cross-sectional structure of BiLaFeO thick film, polarization-electric field ( P- E) loops at various voltages. [ABSTRACT FROM AUTHOR]

We have studied the effect of Bi(MgTi)O additions on the phase formation, structural parameters, microstructure, and dielectric properties of solid solutions in the region of a morphotropic phase boundary in the BiFeO-BaTiO system. Single-phase samples with the perovskite structure have been obtained and the addition of Bi(MgTi)O has been shown to raise the Curie temperature of the ceramics and improve their dielectric properties. [ABSTRACT FROM AUTHOR]

Ceramics of BiBaFeTiO ( x = 0.0625, 0.08125, 0.0875, and 0.11) were prepared according to two doping strategies: one is called single-step doping in which Ba and Ti were doped together in calcination, while the other one is called two-step doping in which Ba and Ti were doped in calcination and sintering, respectively. Compared with samples prepared with single-step doping, those prepared with two-step doping have obviously different XRD patterns and small grains, and are dramatically improved in dielectric loss, resistivity, and remnant magnetization. A low dielectric loss of 0.05 at 10 Hz, a high resistivity of 4×10 Ω·cm, and a large remnant magnetization of 1.5 emu/g, have been obtained simultaneously for BiBaFeTiO prepared with two-step doping. The contrast between these two doping strategies clearly reveals the importance of establishing a proper doping strategy when two or more elements are co-doped to BiFeO. [ABSTRACT FROM AUTHOR]

High-quality BiFeO films have been of great interest for magnetoelectric applications However the fabrication of BiFeO films with large remnant polarization and low leakage current is still rather difficult. In this work, BiFeO-based composite films with different Bi content (BiFeO, 0.7 ≤ x ≤ 1.3) were prepared by pulsed laser position on (001) SrTiO substrates with LaNiO as buffer layer. The dependence of their structure, ferroelectric properties, and exchange bias with NiFe layer on Bi content has been systematically investigated X-ray diffraction patterns show that all films have high (001) orientation, while BiO impurity can be observed in BiFeO with x ≥ 1.1. Clear ferroelectric hysteresis loops can be observed with x > 0.9. The ferroelectric properties have been further improved by Li doping with concentration of 0.03 to suppress the leakage current due to its p-type doping which can compensate the intrinsic n-type conduction. Exchange bias has been observed in all the films with a 3.6-nm-thick NiFe layer The exchange bias field decreases with increasing Bi concentration, but increases by Li doping with concentrations of 0.03 and 0.05. [ABSTRACT FROM AUTHOR]

Nd (3 %) and Ti (2 %) co-doped BiFeO (BNFTO) thin film was deposited on indium tin oxide-coated glass substrate by a metal organic decomposition process. The BNFTO film exhibits a single perovskite phase with random orientation and good insulating property with low leakage current. Asymmetrical polarization-electric field loops are observed in the BNFTO film: This is mainly attributed to the role of oxygen vacancy-related defect complexes in the film. Additionally, the capacitance of the sample is strongly dependent on both the applied voltage and measuring frequency. Furthermore, with the increase in applied voltages or decrease in frequencies, the dielectric tunability is gradually enhanced. The related physics mechanism for the enhanced performance is also discussed. High dielectric constant of 165, dielectric tunability of 27 % and figure of merit of 13.5 are achieved when a measuring frequency of 1 kHz is applied. These present results can be regarded as a base for further development of high-performance BiFeO films. Graphical Abstract: Polarization-electric field ( P- E) and capacitance-voltage ( C- V) curves of the BNFTO film measured under various electric fields and applied bias voltages. [ABSTRACT FROM AUTHOR]

Based on first-principles spin-polarized density functional theory calculations, the relative stability, electronic structures, and magnetic properties of B-, C-, N-, and F-doped BiFeO3 are investigated. The substitution of B, C, N, and F for O produces a magnetic moment of 3.0, 2.0, 1.0, and 1.0 μB per dopant, respectively. The net magnetic moments are from the broken of the symmetry of the AFM spin ordering network. We find that the BiFeO3 with one O atom substituted by a C atom leads to a ferrimagnetic half-metallic property with a C-type spin alignment. The B- and N-doped BiFeO3 are ferrimagnetic semiconductors, and ordered an A-type and a G-type spin alignment, respectively. As for F-doped case, system becomes metallic in its G-type spin alignment. Our study demonstrates that the nonmagnetic elements doping is an efficient route to tune magnetic and electronic properties in BiFeO3. [ABSTRACT FROM AUTHOR]

Mn- and Co-doped and pure BiFeO (BFO) nanoparticles were synthesized through sol-gel method. The result of the Rietveld refinement based on X-ray diffraction (XRD) data revealed that BFO and 10 % Co-doped BFO sample crystallize in rhombohedral symmetry (R3c) structure. The transition of crystal structure can be found when Fe atoms were replaced by Mn atoms partially (from R3c to P4/mbm). Besides, Raman spectra further confirm the structure transformation which is consistent with the results of Rietveld refinements. Analysis of vibrating sample magnetometer (SQUID-VSM) magnetic hysteresis data shows the enhancement of magnetism in Mn- and Co-doped samples which were explained by the changing of bond length and angle which were obtained from the Rietveld refinement. [ABSTRACT FROM AUTHOR]

In this paper, a novel photocatalyst, made up of Ag/BiFeO nanocomposites activated by visible light, was successfully synthesized using a sol-gel process, followed by a chemical reduction method. The as-prepared BiFeO particles and Ag/BiFeO nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and diffuse reflectance spectroscopy. The results showed that the metal Ag nanoparticles with diameter of 20-50 nm are anchored on the surface of BiFeO. Meanwhile, the photocatalytic experiments demonstrated that the Ag/BiFeO composites had excellent photocatalytic activity for the decomposition of methyl orange in visible light, which far exceeded that of the pure BiFeO. These results revealed Ag loading could significantly improve the photocatalytic property of BiFeO. Recycle experiments showed the nanocomposites had an excellent recoverability, suggesting stable photoactivity. Finally, we discuss the photocatalytic mechanism of nanocomposites. The enhanced photoactivity of Ag-decorated BiFeO photocatalyst is most likely attributed to the electronic effect of Ag nanoparticles including surface plasmon resonance. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A series of BiLaFeCuO ( x = 0.01, 0.03 and 0.05) ceramics were synthesized by sol-gel method. The prepared ceramics were characterized by X-ray diffractometer (XRD), vibrating sample magnetometer (VSM) and dielectric measurement. XRD patterns reveal that BiLaFeCuO ( x = 0.01, 0.03 and 0.05) ceramics crystallize in single-phase rhombohedral structure with R3c space group without distortion, and the average crystallite size was in the range of 31-92 nm. VSM exhibited a weak ferromagnetism for La- and Cu-co-doped BiFeO ceramics. The squareness ratio of the hysteresis loop decreases as La concentration increases in BiLaFeCuO. However, these materials show improved dielectric properties compared to undoped BiFeO ceramic. [ABSTRACT FROM AUTHOR]

BiLaFeO ( x = 0.05, 0.1, 0.15 and 0.2) powders and ceramics were prepared by a polyvinyl alcohol (PVA) sol-gel route. Differential scanning calorimetry and thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy and environmental scanning electron microscope were used to characterize the precursors, the derived oxide powders and sintered ceramics. Single-phase BiLaFeO powders were obtained at a temperature as low as 500 °C for 2 h, without the formation of any intermediate phase. All samples were found to be rhombohedrally distorted perovskite structure with a space group of R3c. The effect of La substitution on the dielectric properties of BiLaFeO ceramics was studied over the frequency range of 10 kHz-1 MHz. The real part of permittivity of BiLaFeO samples decreased with the increase of La content. The remnant magnetization M and coercive field H increase with La doping content. A H of as high as 2 × 10 A/m was obtained for BiLaFeO. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Bismuth iron oxide is amongst the class of materials that exhibit simultaneous presence of ferromagnetic and ferroelectric properties with potential applications in spintronic devices. However, there are some problems associated with BiFeO including large leakage current, volatile nature of BiO along with weak ferromagnetic/antiferromagnetic behavior. In order to overcome these difficulties we here report the effect of manganese (Mn) doping on BiFeO (BiFeMnO where x = 0.0-0.3, with interval of 0.05) thin films prepared using sol-gel and spin coating method. X-ray diffractometer (XRD) results show formation of phase pure rhombohedrally distorted perovskite structure. However, with the increase in Mn content, XRD peak positions shift to higher angle indicating reduction in lattice parameters and consequently the unit cell volume. Crystallite size in un-doped and Mn-doped BiFeO films is below cycloidal spin arrangement of BiFeO, i.e. 62 nm. This along with charge compensation mechanism, arising due to replacement of trivalent cation with divalent ion, enhances the magnetic properties of BiFeMnO thin films. Ferromagnetic behavior instead of antiferromagnetic nature of BiFeO is observed in these BiFeMnO thin films for all Mn concentrations. High saturation magnetization of 102 emu/cm was observed for Mn content of 0.2. Dielectric constant increases and the dielectric loss decreases as the dopant concentration is increased resulting in high dielectric constant and low dielectric loss at x = 0.25. The surface work function (wf) has been calculated using Scanning Kelvin Probe technique. The wf results are correlated to the structural and then dielectric properties. [ABSTRACT FROM AUTHOR]

Among the various multiferroic materials bismuth iron oxide is a promising candidate due to its relatively high antiferromagnetic Neel temperature and high ferroelectric Curie temperature as compared to all other multiferroic materials. However, synthesis of phase pure BiFeO is extremely difficult due to the volatile nature of BiO that leads to bismuth-deficient phases and if excess of bismuth is employed it gives rise to bismuth rich phases. Moreover, the synthesis of phase pure BiFeO requires high temperature annealing in the range of 400-700 °C. In order to overcome these difficulties, we here report microwave-assisted sol-gel synthesis of phase pure BiFeO nanoparticles. In the present study, power of microwaves is varied as 136, 264, 440, 616 and 800 W. XRD results show formation of phase pure BiFeO with rhombohedrally distorted perovskite structure at 264, 440 and 800 W. Crystallite size decreases to 21 nm with the increase in microwave power to 800 W. The presence of absorption bands at 470 and 580 cm in FTIR spectra, corresponding to FeO and BiO, indicate the formation of pure BiFeO phase. BiFeO nanoparticles show high dielectric constant (135 at 1 kHz) at 264 W. SEM images show the formation of spherical and cubic nanoparticles in the range of 100-150 nm with microwave powers of 136-440 W. Increasing the microwave power to 616 W gives spherical nanoparticles with sizes of 60 nm while further increasing the microwave power to 800 W results in nanoneedles with diameter of 30 nm. Ferromagnetic behavior, instead of antiferromagnetic nature of BiFeO, is observed for the nanoparticles prepared at microwave power of 616 and 800 W. This demonstrates that microwave-assisted sol-gel technique gives phase pure BiFeO nanoparticles using low power and less time, along with excellent ferromagnetic and dielectric properties as compared to conventional heating method. [ABSTRACT FROM AUTHOR]

Multiferroic materials have attracted great attention due to their potential applications in multifunctional devices. In this work, powders of BiNdFeO (BNFO) with x = 0.00, 0.05, 0.15 and 0.20 were successfully synthesized by a sol-gel method using bismuth nitrate, iron nitrate and neodymium nitrate as sources. The BNFO powders were annealed at 500 °C. X-ray diffraction patterns revealed the formation of single phases BiFeO and BNFO. We observed that the neodymium substitution leads to the change of the BiFeO crystal structure from rhombohedral with space group R3c (α-phase) to pseudo-cubic symmetry Pm3 m. A high temperature variety (γ-phase) of multiferroic BiFeO compound has been stabilized for 15 % of neodymium content. The morphology of the particles seemed to be approximately spherical, the particle size of the BNFO is between 23 and 67 nm. Those powders show both magnetic transition at Neel temperature (T) and ferroelectric transition around Curie temperature (T). In addition a clear ferromagnetic component is observed for all powders. The variations of dielectric constant and dielectric loss, proves a possible coupling between the electric and magnetic dipole in these systems. [ABSTRACT FROM AUTHOR]

Pure BiFeO (BFO) and Cr-doped BiFe Cr O (BFCO) thin films were successfully prepared on F-doped SnO conductive film (FTO)/glass (SnO : F) substrates by a sol-gel method. The effect of Cr doping on the structure, ferroelectric, and ferromagnetic properties of the BFO and BFCO thin films have been investigated. X-ray diffraction, Rietveld refined X-ray diffraction (XRD) patterns, and Raman spectroscopy results clearly reveal that the BFCO thin film is characterized by the coexistence of two phases (trigonal and tetragonal). Moreover, the various leakage mechanisms of both thin films have also been studied. The improved ferroelectricity with remnant polarization (Pr) of about 2Pr = 68.68 μC/cm under an applied electric field of 1,181.8 kV/cm and enhanced ferromagnetism with saturation magnetization ( M) of M = 0.93 emu/cm have been observed in the BFCO thin film. The improved electrical properties of the BFCO thin film are ascribed to the coexistence of trigonal and tetragonal phase and high valence of Cr , and the Fe-O octahedron distortion is enhanced due to the overlap and hybridization of Fe /Cr and O orbits by Cr doping. [ABSTRACT FROM AUTHOR]

Perovskite-type BiFeO nanoparticles have been synthesized by thermal decomposition of glyoxylate precursor. The effects of different thermal decomposition temperatures (300-600 °C) on the phase evolution, morphology, and physical properties were investigated by thermal analysis, infrared spectroscopy, X-ray diffraction, electron microscopy, vibrating sample magnetometry, and UV-Vis spectroscopy methods. The high purity bismuth ferrite nanoparticles synthesized at 600 °C showed the weak ferromagnetism behavior, due to the size confinement effect. Furthermore, the BiFeO nanoparticles also exhibited strong absorption in the visible region with the lowest band gap of about 2.08 eV. [ABSTRACT FROM AUTHOR]

Mn-modified 0.67BiFeO-0.33BaTiO (BF-BT) bulk ceramics were prepared via a solid-state reaction process using quenching method. The X-ray diffraction peaks shifted toward higher angles as increasing Mn content. Ferroelectric properties were improved by a small amount of Mn content. Leakage current density of 1 mol% Mn-modified ceramic showed the lowest leakage current density, 9.74 × 10 A/cm at 30 kV/cm. The value of small- and large-field piezoelectric coefficients ( d and d *) were 135 pC/N and 250 pm/V, respectively, in 1 mol% Mn-modified BF-BT ceramic. A small amount of Mn content was effective to improve electrical properties and sintering behavior in Mn-modified BF-BT system. [ABSTRACT FROM AUTHOR]

We report on preparation of BiCaFeO ( x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) thin films using a cost-effective and lower temperature sol-gel process. Structural, optical and magnetic properties are studied for the films annealed in vacuum in presence of magnetic field (500 Oe) at 300 °C for 60 min. X-ray diffraction results show rhombohedrally distorted perovskite structure of BiFeO in un-doped and doped films. Structure is seen to be affected by the charge compensation mechanism (oxygen vacancies) caused by replacement of trivalent ion (Bi) with divalent anion (Ca). Smaller crystallite size (~25.8 nm) with minimum stacking fault probability is observed for x = 0.2. Addition of Ca forms localized states within the forbidden band thus leads to a decrease in direct band gap from 2.7 to 2.4 eV. Ferromagnetic behaviour is observed for all the calcium (Ca) doping concentrations in BiFeO thin films. High saturation magnetization ( M) of ~130 emu/cm is observed for the dopant concentration of 0.2. [ABSTRACT FROM AUTHOR]

Due to its unique properties, bismuth ferrite (BiFeO, BFO) has gained a great deal of interest. The prevalence of BFO increases the likelihood of exposures either to environment or to humans. Unfortunately, the understanding of BFO biological effects is very limited. In this study, a battery of standard tests, such as morphology observation, MTT, and LDH assay, and flow cytometry analysis, was employed to elucidate in vitro cytotoxicity of BFO nanoparticles (NPs) in the size range of 30-90 nm using PC12 cells as a model. The results show that BFO-NPs could tightly attach to the cell membrane in the culture medium, which significantly affect the cell adhesion and inhibit their proliferation. Moreover, cytotoxicity of BFO-NPs is greatly mitigated when the exposure time was extended to 48 h. These findings suggest that BFO-NP possess the nature of acute cytotoxicity since the cells can recover to a certain extent over with incubation time. For the first time, our study reveals some essential properties of BFO-NP toxicity, which may advance BFO applications and its toxicological study. [ABSTRACT FROM AUTHOR]

BiBaFeO and BiBaFeTiO ceramics have been synthesized by a tartaric acid modified sol-gel method. BiBaFeO has a pseudo-tetragonal structure, while triclinic distortion was induced by the 0.05 Ti substitution from the Rietveld refinements on the X-ray diffraction patterns. The addition of Ti significantly reduced the leakage current. Compared with the remnant magnetization ( M=0.001 emu/g) and coercivity ( H=80 Oe) of pure BiFeO, the M and H of BiBaFeO are strongly enhanced to 0.16 emu/g and 4.2 kOe, respectively. The Ti substitution has little influence on the magnetic properties. From the temperature-dependent magnetization and differential scanning calorimeter measurements, we conclude that the enhanced ferromagnetism in Ba doped BiFeO might be attributed to the trace impurity of BaFeO. [ABSTRACT FROM AUTHOR]

BiFeO (BFO) thin films of thickness about 800 nm deposited on Si (100) substrates by sol-gel spin coating method were irradiated by 200 MeV Ag ions. Modification of structure and surface morphology of the films under irradiation was studied using glancing incidence X-ray diffraction (GIXRD) and atomic force microscope (AFM). Fluence dependence of GIXRD peak intensity indicated formation of 10 nm diameter cylindrical amorphous columns in crystalline BFO due to 200 MeV Ag ion irradiation. AFM analysis indicated that the pristine film consists of agglomerated grains with diffuse grain boundary. Irradiation led to reduced agglomeration of the grains with the formation of sharper grain boundaries. The rms roughness ( σ) estimated from AFM analysis increased from 6·2 in pristine film to 12·7 nm when the film irradiated at a fluence of 1 × 10 ions cm. Further irradiation led to decrease of σ which finally saturated at a value of 7-8 nm at high ion fluences. The power spectral density analysis indicated that the evolution of surface morphology of the pristine film is governed by the combined effect of evaporation condensation and volume diffusion processes. Swift heavy ion irradiation seems to increase the dominance of volume diffusion in controlling surface morphology of the film at high ion fluences. [ABSTRACT FROM AUTHOR]

In this work, we report the influence of Co-doping on the electronic band structure, dielectric and magnetic properties of LaBiFeCoO ceramics. X-ray photoelectron spectroscopy investigation shows that Co dopant can shift the valence band spectrum and core-level lines of constituent elements towards higher bind energy regions simultaneously increase the concentration of oxygen vacancies in ceramics. The effects of dopant are discussed with focus given to the Co-doping induced enhancement of electrical conductivity and resistive switching phenomena. [ABSTRACT FROM AUTHOR]

BiFeO nanofibers doped with Ba and Mn have been prepared by an electrospinning method. The influence of Ba doping on the phase composition, microstructure, photocatalytic properties was investigated detailedly. Our results indicate that with the increase of Ba doped contents, the formation of impurity phase can be suppressed in these BiFeO nanofibers. A crystal lattice transformation occurred when 15 % Ba was doped. The degradation of Congo Red proved the enhanced photocatalytic behaviors in visible light region can be observed in these BFO nanofibers. [ABSTRACT FROM AUTHOR]

Effects of rare earth Dy and transition metal ( TM = Cu, Co and Mn) ions co-doping on the structural, electrical and ferroelectric properties of the BiFeO thin films prepared on Pt(111)/Ti/SiO/Si(100) substrates by using a chemical solution deposition method were investigated. All thin films formed as randomly oriented polycrystalline, with no detectable impurity or secondary phases. Among the thin films, the (BiDy)(FeMn)O thin film exhibited well saturated hysteresis loops with remnant polarization (2 P) of 51 μC/cm and low coercive electric field (2 E) of 685 at 935 kV/cm and low leakage current density of 1.4 × 10 A/cm at 100 kV/cm. The enhanced properties observed in the co-doped thin films could be considered as being the results of the suppression of ionic defects and of the modified microstructure. [ABSTRACT FROM AUTHOR]

BiFeZnO thin films ( x=0, 0.05, 0.1, 0.2, and 0.3) were prepared on LaNiO buffered surface oxidized Si substrates using pulsed laser deposition. The effect of Zn dopants on the structural, electrical, magnetic properties, and exchange bias on NiFe layers for BiFeO thin films has been systematically investigated. X ray diffraction and Raman spectra show that BiFeZnO thin films have polycrystalline rhombohedral structure with Zn concentration smaller than 5 %, and a large amount of the impurity phase of BiFeO with further increasing Zn concentration above 10 %. With 5 % Zn doping in BiFeO, the film quality is improved with larger grain size, better ferroelectricity, and larger magnetization. The exchange bias of BiFeZnO on a 3.6 nm thick NiFe layer drastically decreases with increasing Zn doping concentration, and totally disappears with the Zn concentration larger than 10 %, indicating that the canted antiferromagnetic spin structure of BiFeO was suppressed with increasing the Zn doping concentration. [ABSTRACT FROM AUTHOR]

Ordered BiFeO (BFO) and BiFeCoO (BFC) nanotubes arrays were successfully synthesized by a sol-gel anodic aluminum oxide template method. Both kinds of nanotubes had straight and smooth profiles with diameters of about 200 nm and wall thicknesses of about 20 nm. A perovskite-type structure of BFO was confirmed in these nanotubes by high-resolution transmission electron microscopy. The dielectric properties of these nanotube arrays were measured and larger permittivity was obtained for the BFC nanotubes via adopting a columnar composite structure model. Ferromagnetic measurement showed enhanced ferromagnetism for the sample with Co doping. These improvements in dielectric constant and ferromagnetism of the nanotubes by Co doping may be mainly attributed, respectively, to the lattice distortion and the breakage of the spin cycloid period of the BFC nanotubes. [ABSTRACT FROM AUTHOR]

Highly preferentially oriented polycrystalline BiFeO thin film was grown on FTO/glass substrate by a sol-gel method annealed at 500 °C. XRD result showed that the film adopts highly (100) preferential orientation. SEM results indicate that the film is composed of large grains of 40-200 nm and the thickness is about 320 nm. Room temperature saturated polarization and large Pr ~55 μC/cm were obtained. Leakage current was substantially reduced by the controlling of ferroelectric polarization. Polarization-modulated conduction mechanism was studied. Moreover, substantial photovoltaic effect was observed. [ABSTRACT FROM AUTHOR]

Phase pure multiferroic BiFeO (BFO) was prepared by the co-precipitation technique using diverse precursors at a temperature as low as 400 °C. The dependence of structural and dielectric properties was investigated with the variation of pH (8-13, with steps of 1). Uniaxially pressed powders were sintered in air at 500 °C for 2 h. X-ray diffraction analysis determined the amorphous nature of the as-synthesized samples and the perovskite nature of the sintered samples. The crystal structure obtained from the lattice parameters of the BFO specimens was R3c hexagonal. The fractional porosity of the pellets was determined from the measured and theoretical density of the samples. The crystallite size varies from 48-62 nm with the variation of the pH value. SEM micrographs exhibited a grain morphology and a wide size distribution. The dielectric constant, loss tangent, and ac conductivity of the pellets were measured as a function of frequency (20 Hz-3 MHz). A high dielectric constant and dissipation factor for the sample prepared with pH=10 was observed in the low frequency range. [ABSTRACT FROM AUTHOR]