BiFeO3 Powders Research Articles

Synthesis of pure phase BiFeO3 powders by direct thermal decomposition of metal nitrates

Pure phase BiFeO3 powders were successfully synthesized by direct thermal decomposition of metal nitrates at 500°C. The as-prepared BiFeO3 had a perovskite structure which was studied using X-ray diffraction. The porous structures were investigated through scanning electron microscopy. Morphology of BiFeO3 changed from micron-sized porous structures to nano-sized particles as NH3HCO3 was added. Furthermore, the mechanism of formation of BiFeO3 was also discussed through X-ray diffraction, thermogravimetry and differential scanning calorimetry. The optical absorption band gap of the micro-sized porous structure BiFeO3 is 1.8eV.

Dielectric and ferroelectric properties of BiFeO3 ceramics sintered in different atmospheres

Pure BiFeO3 powders were successfully synthesized by microwave-hydrothermal processing, and the pellets were sintered in different atmospheres. The properties of BiFeO3 ceramic samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), dielectric measurements (LCR) and polarization-field hysteresis loop. The effects of different atmospheres (including air, N2, O2 and H2) on ferroelectric properties of BiFeO3 ceramics were studied in this paper. The results show that the BiFeO3 ceramics sintered in H2 and N2 atmosphere have a single-phase rhombohedra distorted perovskite structure with no trace of other impurity phases. The dielectric properties of BiFeO3 ceramics were greatly influenced by O2 and H2 atmospheres. The samples sintered in H2 atmosphere have the highest dielectric constant. Polarization-field hysteresis loops measured at room temperature indicated the samples sintered in H2 and N2 atmospheres have higher spontaneous polarization and lower breakdown field, but the ferroelectric properties of samples sintered in O2 atmospheres were poor.

Low Temperature Synthesis, Structural, Optical and Magnetic Properties of Bismuth Ferrite Nanoparticles

Phase pure nanosized BiFeO3 (BFO) powder was synthesized by sol–gel method based on the propylene glycol‐gel reaction. The formation mechanism, crystal structure, magnetic and optical properties were investigated by thermogravimetry, differential thermal analysis, infrared spectroscopy, X–ray diffractometry, Rietveld analysis, Raman spectroscopy, transmission electron microscopy, SQUID magnetometry and ultraviolet–visible spectroscopy. X–ray diffraction and Raman studies revealed the formation of pure and well‐crystallized BFO nanocrystallites at a low temperature of 400°C. The BFO nanoparticles showed weak ferromagnetic property at room temperature due to size‐confinement effects. The UV–visible spectra showed strong band‐gap absorption at ~590 nm (2.1 eV) for BFO nanoparticles suggesting their potential application as visible‐light‐response photocatalyst.

Tunable morphology and optical absorption of bismuth ferrite synthesized by sol–gel–hydrothermal method

Bismuth ferrite BiFeO3 (BFO) powders with various morphologies were successfully prepared via a sol–gel–hydrothermal synthesis process. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Microspheres and microcubes were obtained as Bi–Fe–glycerol sol was used as precursor, and submicrometer-sized particles could be prepared by using Bi–Fe–glycerol gel. Possible formation mechanism of BFO microcrystals was proposed in this work. Moreover, the results of UV–vis diffuse reflectance spectroscopy reveal that BFO powders can be used as an effective photocatalyst under visible light in addition to its ferroelectric and magnetic applications.

Structure and phase transition of BiFeO3 cubic micro-particles prepared by hydrothermal method

Single-phase bismuth ferrite (BiFeO3) powders were synthesized with a hydrothermal method by controlling the experimental conditions carefully. The powder structure, morphology and composition were characterized by using X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscope, Raman measurement and X-ray photoelectron spectroscopy. The particles change from irregular agglomerations to regular cubes with increasing KOH concentration. The large BiFeO3 cubic particles enjoy much smooth surfaces with well-matched element ratio (Bi:Fe:O=1:1:3) and chemical valence (Bi3+, Fe3+ and O2−). The high temperature XRD and differential scanning calorimetry show that BiFeO3 powders have a hexagonal perovskite structure with a space group R3c below 370°C and a rhombohedral structure with a space group R3m below 755°C. BiFeO3 undergoes a phase transition in the temperature range of 755–817°C from rhombohedral structure to a cubic phase, then decomposes to liquid and Fe2O3 above 939°C.

The Effect of Heat Treatment on Structural and Multiferroic Properties of Phase-Pure BiFeO3

Phase-pure multiferroic BiFeO3 (BFO) was prepared by the coprecipitation technique using diverse precursors bismuth oxide at temperature as low as 400°C. The dependence of structural, microstructural, thermal, electrical (AC and DC), and magnetic properties on sintering temperature was systematically investigated. Uniaxially pressed samples (O8 mm) were sintered in air at 500°C to 800°C for 4 h. X-ray diffraction analysis was used to determine the amorphous and perovskite nature of as-synthesized and calcined/sintered samples, respectively. The crystallite size of sintered powders increased from 47 nm to 67 nm. Scanning electron microscopy showed grain growth during sintering, which improved intergranular connectivity and decreased porosity in the samples. The ferroelectric to paraelectric Curie transition temperature (TC) of pure BFO powder was detected by differential scanning calorimetry analysis and found to be 820°C ± 1°C. The samples exhibited high AC resistivity and dielectric constant, and low loss tangent values. The samples exhibited weak ferromagnetic behavior with an unsaturated magnetization versus magnetic field hysteresis loop at room temperature. Ferroelectric behavior and variation in remnant polarization and coercivity were observed from polarization versus electric field loops. Enhanced capacitance in the magnetic field revealed the magnetoelectric effect in the samples.

Phase transitions of pure and Ba-doped BiFeO3 under high pressure

In order to evaluate the effect of impurity substitution on phase transition of BFO, we report high-pressure X-ray diffraction experiments on pure and Ba-doped BiFeO3 powders in diamond-anvil cells up to 18.7GPa. A low-temperature hydrothermal synthesis route was utilized to fabricate these two samples. The experimental results reveal that two structural phase transitions take place in these two different samples in the investigated pressure range. As two ADXRD data sets are compared, it is shown that the intermediate phase II is not detected in Ba-doped sample. In addition, modifications in phase transition behavior and compressibility due to a minor Ba incorporation highlight the high sensitivity of BFO to variations of chemical composition.

Effect of Sintering Temperature on Nanostructured Multiferroic BiFeO<sub>3</sub> Ceramics

Nanostructured multiferroic BiFeO3 (BFO) powders were synthesized by using the co-precipitation method. Calcination of acquired powder was carried out at 400°C for 3h. Uniaxially pressed pellets were sintered at 500°C, 600°C, 700°C and 800°C for 2 hours in air. These samples were characterized for structural, thermal, electrical and magnetic properties. X-ray diffraction (XRD) confirmed the amorphous nature of the as driven powder and phase purity of the calcined BFO sample. The crystallite size varied with the sintering temperature from 52 to 70 nm. Sintering above 500°C induced impure phases due to oxygen vacancies and volumetric strain in crystal structure. Ferroelectric to paraelectric transition temperature TC~815°C was verified by the differential scanning calorimetry (DSC). Surface morphology and grain growth was observed using scanning electron microscopy (SEM). Electrical ac measurements were performed in the frequency range from 20 Hz to 3 MHz at room temperature. For a particular sample, capacitance decreased and susceptance increased with the increase of applied frequency signal. These parameters were increased with the increase of sintering temperature. Vibrating sample magnetometer (VSM) revealed the diverse weak ferromagnetic behavior for the samples sintered at different temperatures. Maximum coercivity (Hc~119.2 Oe) and maximum remnant magnetization (MR~2.1x10-3 emu/g) were obtained for the sample sintered at 700°C for 2hr.

Structure evolution and photocatalytic activity of BiFeO3 powders synthesized by hydrothermal decomposition of metal-EDTA complexes

In the paper, the formation mechanism for pure phase BiFeO3 (BFO) in an EDTA-assisted hydrothermal process with the presence of NaNO2 was investigated in detail. The analysis revealed that the hydrothermal decomposition of Fe-EDTA complexes with the presence of NaNO2 intensely influenced both the crystal structure and morphology of BFO powders. Moreover, pure BFO particles exhibited efficient photocatalytic activity under visible-light irradiation, suggesting their promising applications as photocatalysts.

Effect of magnetic annealing on magnetization of BiFeO3 ceramics

The effect of magnetic annealing treatment on the magnetization of multiferroic BiFeO3 was studied systematically. A series of pelletized nano-sized BiFeO3 powders were annealed at high temperature under different magnetic fields. Typical ferromagnetic hysteresis loops were obtained at room temperature of the ceramics which were derived from ferromagnetic BiFeO3 precursors. On the other hand, antiferromagnetic behaviors were observed in other samples synthesized from nonmagnetic precursors. The enhanced magnetic properties were ascribed to the magnetic anisotropy which was induced by the strong magnetic fields. This work indicates that the strong magnetic annealing method is an alternative approach to tuning the magnetic properties of high performance multiferroic materials with canted antiferromagnetic ordering.

Decomposition behavior and dielectric properties of Ti-doped BiFeO3 ceramics derived from molten salt method

The effects of Ti-doping on the decomposition behavior, crystal structure, sintering behavior and dielectric properties have been investigated for the Ti-doped BiFeO3 ceramics derived from molten salt method. XRD reveals the almost pure phase BiFeO3 is synthesized in the Ti-doped BiFeO3 powders. And the particle size of Ti-doped BiFeO3 powers obviously decreases with the increase of Ti content. However, the sintering temperature elevates significantly after Ti-doping. The DC resistivity can enhance by up to four orders of magnitude (from 104 to 108 Ωm) with only 5 at% Ti doping. But the dielectric constant is suppressed from 104 to 102, and dielectric loss obviously reduces with a small amount of Ti doping. The variation of dielectric properties has been discussed from the decomposition of BiFeO3 phase. The Ti-doping can effectively suppress the decomposition reaction in Ti-doped BiFeO3 ceramics.

Self-assembly growth of flower-like BiFeO3 powders at low temperature

In this work, flower-like BiFeO3 powders were synthesized by a hydrothermal method at low temperature. The effects of mineralizer, reaction temperature and soak time on the crystal phase structure and morphology of the BiFeO3 powders have been investigated. Perovskite BiFeO3 powders were obtained as the concentration of KOH is 1–6 mol/L. The SEM images of BiFeO3 powders which synthesized at 150 °C for 1 h with 2 mol/L KOH exhibit cubic morphology. Whereas, the powders prepared for 6 h show flower-like morphology.

Effect of Praseodymium Species on the Structural and Functional Properties of Nanocrystalline BiFeO3 Powders and Thin Films

ABSTRACTThe present study addressed the effect of the incorporation of Praseodymium species in the BiFeO3(BFO) structure on the corresponding structural and functional properties of powders and films. The level of the doping species varied from 0 at% to 4 at%. BFO powders and thin films were synthesized by a sol-gel method, where glycol was aggregated to the main solvent to increase the viscosity of the precursor solutions and promote their adhesion onto platinum substrates. The development of the host BFO structure was confirmed by XRD analyses of samples annealed at 700°C for one hour (powders) or 500°C for 2 hours (thin films), in air. The average crystallite size varied from 37 nm to 41 nm and 28nm to 40nm for powders and thin films, respectively, due to the increase of the doping level. The incorporation of specific dopant species played an important role in the ferromagnetic and ferroelectric behavior in the material.

Oriented Growth of Bi2Fe4O9 Crystal and its Photocatalytic Activity

Oriented growth of Bi2Fe4O9 crystals were synthesized by a facile hydrothermal route in the presence of different organic additives. X-ray diffraction was used to characterize the derived powders, indicating that single-phase Bi2Fe4O9 with growth orientation along the (001) and (221) planes were obtained respectively. Extensive structural characterization of the as-prepared samples was observed using Fourier transform infrared spectroscopy, Scanning electron microscope, and UV-vis diffuse reflectance spectrum. The photocatalytic activity of Bi2Fe4O9 powders with different orientation was evaluated on degradation of methyl orange solution under visible light irradiation. The results show that the photocatalytic activity of the (001) plane is much higher than that of the (221) plane.

Synthesis of Multiferroic BiFeO<sub>3 </sub>Powders by Sol-Gel Auto-Combustion

Crystalline multiferroic BiFeO3 powders were directly synthesized by sol-gel auto-combustion method. The gels, derived from the solutions of 2-methoxyethane, metal nitrate and citric acid, exhibited the self-propagating combustion behaviors at ambient temperature when it is ignited in air. After auto-combustion, the dried gels transformed into crystalline BiFeO3 powders and no further calcination was needed. The nature of auto-combustion was ascribed to heat-induced redox between NH4NO3 and carboxyl group. The TG-DTA was carried out to study the auto-combustion of dried gels. The synthesized powders were characterized by XRD and SEM techniques.

Bismuth Ferrite Nanopowders Prepared by Sol-Gel

BiFeO3 powders were prepared by sol-gel process and calcined at different temperatures. The DTA curve shows an obvious exothermic peak near 480.5°C, the temperature close to BiFeO3 formation temperature, which is agreement with the XRD results (450°C). After calcining at 600°C for 1h, XRD spectra has the emergence of several sharp diffraction peaks, compared with the standard XRD spectrum of the crystal BiFeO3. As the calcining temperature increased, the diffraction peak intensity of the XRD spectra of BiFeO3 gradually increased and the diffraction peaks became sharply, indicating that the grain size gradually became larger. There is a clear endothermic peak near 825.1°C, which is the α phase to β phase transition from the knowledge of the phase diagram and in good agreement with the reported Curie temperature.

Synthesis and dielectric properties of BiFeO3 derived from molten salt method

BiFeO3 powder was synthesized in NaCl media at temperature range from 700 to 800 °C, using Bi2O3 and Fe2O3 as raw materials. Effects of calcining temperature and salt ratios on the synthesis of BiFeO3 powder had been investigated. It was found that NaCl effectively promoted the formation of BiFeO3. Almost pure BiFeO3 phase with a very small amount of Bi2Fe4O9 phase was synthesized at 750 °C with salt weight ratios of 1:1. A large amount of BiFeO3 phase decomposed to Bi2Fe4O9 and Bi25FeO39 phase when the temperature was up to 800 °C. In the present method, the calcining temperature played an important role in the formation of BiFeO3 phase. BiFeO3 ceramics derived from molten salt method were prepared and exhibited the higher dielectric constant.

Controllable Microwave Hydrothermal Synthesis of Bismuth Ferrites and Photocatalytic Characterization

The process, by which three kinds of bismuth ferrites (BiFeO3, Bi25FeO40, and Bi25FeO40–BiFeO3) were synthesized for 1 h through a microwave hydrothermal method by changing the KOH concentration and the temperature, is summarized in this article. The as‐prepared bismuth ferrite powders were characterized by the X‐ray diffraction, the field emission scanning electron microscopy, and the transmission electron microscope, and the band gaps, specific surface areas, photocatalytic and magnetic properties were explored as well. The results showed that the degradation degree of methyl orange using BiFeO3, Bi25FeO40, and Bi25FeO40–BiFeO3 as catalyst were 35%, 52%, and 90% at 2 h, respectively, and the magnetizations of the three powders were 0.07, 3.17, and 0.55 emu/g, respectively. This indicated that the porous cubic Bi25FeO40–BiFeO3 powder has the best photocatalytic property of the three, making it useful as a new type of photocatalytic material which can be easily recycled by magnetic separation.

Fabrication of BiFeO3//Bi4Ti3O12 Composites

In this study a method of fabrication of ceramic-ceramic composites with 0-3 connectivity was developed and BiFeO3//Bi4Ti3O12 (BF//BiT) ceramic composites were fabricated for different concentrations of the ceramic phases. BiFeO3 and Bi4Ti3O12 ceramic powders were first synthesized by the conventional mixed oxide method (MOM). Then BF powder was dispersed in a BiT ceramic powder, and next such composite was pressed and sintered. A free sintering method was utilized. Properties of the BF//BiT composites were studied in terms of their density, crystalline structure (X-ray diffraction) and surface morphology (SEM). It was found, that bismuth ferrite powder crystallized in rhombohedral symmetry and bismuth titanate crystallized in monoclinic phase for cV = 2% of BiFeO3 and orthorhombic phase for cV = 4% and cV = 6% of BiFeO3 component of the composite. Apparent density of the composites varied within the range ρ = (6.2–6.6) × 10−3 kg/m3. Clear change in surface morphology was found for the composites under study.

Size-controlled synthesis of BiFeO3 nanoparticles by a soft-chemistry route

In this work we report the size-controlled synthesis of BiFeO3 nanoparticles via a soft-chemistry route. In this route, the aqueous solution of inorganic Bi and Fe salt is gelled by using acrylamide and bisacrylamide. It is demonstrated that the grain size of resulted BiFeO3 powders can be tailored by varying the ratio of acrylamide to bisacrylamide. With increase in the bisacrylamide content, the grain size decreases monotonously. By using this method, a series of BiFeO3 samples with average grain size ranging from 110 to 52 nm have been prepared. The thermal decomposition process of precursor xerogels and the formation of BiFeO3 phase are investigated by means of X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry analysis, and fourier transform infrared spectroscopy (FTIR). SEM observations reveal that the prepared BiFeO3 nanoparticles are nearly spherical in shape with a narrow diameter distribution. Magnetic hysteresis loop measurement shows that the BiFeO3 nanoparticles exhibit weak ferromagnetic behavior at room temperature, and a saturation magnetization of ~1.56 emu/g is achieved for the 52 nm sample.