Pristine BiFeO3 Research Articles

Fabrication, Structure, and Magnetic Properties of Pure-Phase BiFeO₃ and MnFe₂O₄ Nanoparticles and their Nanocomposites

We fabricated pure-phase BiFeO₃ (BFO) and MnFe₂O₄ (MFO) nanoparticles as well as their nanocomposites (BMFO), and then we studied their structures and magnetic properties. Pristine BFO nanoparticles of 93.3 nm average diameter were successfully synthesized using the sol-gel method by varying the solvent condition and the precursor amount. Pristine MFO nanoparticles with a mean diameter of 70.5 nm were synthesized using the co-precipitation method entailing the optimization of the preheating and aging steps. The fabricated MFO nanoparticles showed mostly nanospheres with few nanocubes. The nanocomposite samples of 50 % MFO and 50 % BFO were fabricated through grinding and pelletization, followed by sintering under an inert atmosphere. The crystal structures of the pristine materials in the nanocomposites were well preserved. The magnetization values (Ms) of the BFO, MFO, and BMFO were 4.9, 52, and 33 emu/g, respectively. This latter Ms value was significantly higher than that of BFO, owing to the coexistence of FeSUP2+/SUP and FeSUP3+/SUP in its BFO phase and the incorporation of magnetic MFO. Two synthesis methods and material properties including the structural, morphological, magnetic, and oxidation states of the BFO-MFO nanocomposites were studied in order to achieve a high Ms value of 33 emu/g, which is higher than the bulk values of previously reported BFOMFO composite samples.

Unraveling the structural and composition properties associated with the enhancement of the photocatalytic activity under visible light of Ag2O/BiFeO3-Ag synthesized by microwave-assisted hydrothermal method

BiFeO3 is synthesized for the first time via a microwave-assisted hydrothermal method along with a thermal treatment to incorporate Ag nanoparticles (Ag2O/BiFeO3-Ag). SEM and TEM micrographs demonstrate that Ag nanoparticles are homogenously dispersed on BiFeO3, while XRD reveals a reduction in size of the average crystallite size when Ag is impregnated on the material in comparison with the pristine BiFeO3 phase. Raman analysis indicates the substitution of Bi by Ag atoms into the lattice, while XPS analysis discloses the presence of Ag0 and Ag2O in the catalyst. Ag2O/BiFeO3-Ag exhibits superior photocatalytic activity compared with BiFeO3 based on the degradation of 10.4 µmol L−1 Rhodamine B (RhB) under simulated visible light irradiation. The enhancement on the photocatalytic performance was attributed to a surface plasmon resonance effect efficiently transferring photogenerated electrons from BiFeO3 to Ag0, and photogenerated holes from a heterojunction formed between BiFeO3 and Ag2O. An energy diagram of the system is established based on the band-gap, conduction and valence bands of BiFeO3 and Ag2O. The stability of the Ag2O/BiFeO3-Ag catalyst leading to RhB-photodegradation was monitored during six consecutive cycles. Experiments conducted with scavengers (isopropyl alcohol, ascorbic acid and coumarin) reveal hydroxyl radical formation as the primary oxidant species of RhB.

Enhancement of the photoelectrochemical water splitting by perovskite BiFeO3via interfacial engineering

Ferroelectric semiconductors like BiFeO3 are increasingly being investigated for applications in solar energy conversion and storage due to their intrinsic ability to induce ferroelectric polarization-driven separation of the photogenerated charge carriers resulting in above-bandgap photovoltages. Nevertheless, the BiFeO3 has been commonly prepared using complex and expensive fabrication techniques, e.g., epitaxial growth, radio frequency sputtering and pulsed laser deposition, which are not economically viable for large-scale production. Herein, we report a facile and scalable method for the fabrication of porous perovskite BiFeO3 photoanodes, as well as sequential interfacial engineering methods to enhance their photoelectrochemical performance for water splitting. Upon atomic layer deposition of a TiO2 overlayer and photo-assisted electrodeposition of a cobalt oxide/oxyhydroxide co-catalyst, the photocurrent density of the engineered photoanode for oxygen evolution reaction (1 M NaOH) significantly increased from negligible photocurrent of the pristine BiFeO3 to 0.16 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under simulated 1 sun irradiation (100 mW cm−2, AM1.5G spectrum). Furthermore, such functionalization of the BiFeO3 photoanodes shifts the photoelectrochemical oxidation onset potential by 0.7 V down to 0.6 V vs. RHE. The significantly enhanced photoelectro-oxidation activity is facilitated by the improved charge transfer and electrochemical kinetics.

Fabrication of visible light active BiFeO3/CuS/SiO2 Z-scheme photocatalyst for efficient dye degradation

A novel Z-scheme photocatalyst BiFeO3/CuS/SiO2 was fabricated by hydrothermal technique and test for methyl orange photodegradation under visible light. 99% of methyl orange dye was degraded in 60 min which was higher than the photocatalytic activity of pristine BiFeO3 and CuS. OH and O2̅ were the main reactive species during degradation process. The formation of heterojunction promoted rate of electron hole pair separation, effective exploitation of visible light absorption and thus improved the photocatalytic activity. Besides, BiFeO3/CuS/SiO2 showed a significant recycling efficiency over six catalytic cycles.

Effect of cobalt-doping on dielectric, magnetic and optical properties of BiFeO3 nanocrystals synthesized by sol – gel technique

BiFe1-xCoxO3 (x = 0.00, 0.01, 0.03, 0.05 and 0.07) nanoparticles (NPs), were prepared by ethylene-glycol-based sol-gel technique. Phase purity of the NPs was confirmed by x - ray diffraction (XRD) technique. The average size of pristine BiFeO3 (BFO) NPs was found to be 46 nm, which initially increased to 50 nm for 1% Co doping and then decreases to 48, 45 and 43 nm for 3%, 5% and 7% Co-doped BFO NPs, respectively. X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy confirmed that the oxidation state of Fe and Co is +3. In the low frequency region, the dielectric constant (ε‘) shows a maximum decrease by 96% (137 → 5.1) on 5% Co-doping concomitant with 62% decrease in dielectric loss (0.32 → 0.12) which indicates substantial reduction in leakage current density. Further, the pristine BFO shows a well-defined dielectric loss peak at 40 Hz (tan δ = 0.4). In contrast, twin dielectric loss peaks are uniquely observed for all the Co doped BFO NPs. 1% doped NPs show first and second peaks at 7 Hz and 20,400 Hz, respectively, which shifts to higher frequencies of 245 Hz and 154,000 Hz, on 5% doping. The magnetic measurements (M − H) revealed the ferromagnetic behaviour of the NPs. On Co doping, saturation magnetization (Ms) increased with decrease in coercive field (Hc). A maximum enhancement of 226% (0.93 → 3.05 emu/g) in Ms values concomitant with decline of 61% in Hc values (80 → 15 Oe) was observed for 7% doping. The reduction in leakage current and enhancement of magnetic properties makes the NPs better-suited for device applications.

Maximizing Short Circuit Current Density and Open Circuit Voltage in Oxygen Vacancy-Controlled Bi1-xCaxFe1-yTiyO3-δ Thin-Film Solar Cells.

Designing solid-state perovskite oxide solar cells with large short circuit current (JSC) and open circuit voltage (VOC) has been a challenging problem. Epitaxial BiFeO3 (BFO) films are known to exhibit large VOC (>50 V). However, they exhibit low JSC (≪μA/cm2) under 1 Sun illumination. In this work, taking polycrystalline BiFeO3 thin films, we demonstrate that oxygen vacancies (VO) present within the lattice and at grain boundary (GB) can explicitly be controlled to achieve high JSC and VOC simultaneously. While aliovalent substitution (Ca2+ at Bi3+ site) is used to control the lattice VO, Ca and Ti cosubstitution is used to bring out only GB-VO. Fluorine-doped tin oxide (FTO)/Bi1-xCaxFe1-yTiyO3-δ/Au devices are tested for photovoltaic characteristics. Introducing VO increases the photocurrent by four orders (JSC ∼ 3 mA/cm2). On the contrary, VOC is found to be <0.5 V, as against 0.5-3 V observed for the pristine BiFeO3. Ca and Ti cosubstitution facilitate the formation of smaller crystallites, which in turn increase the GB area and thereby the GB-VO. This creates defect bands occupying the bulk band gap, as inferred from the diffused reflection spectra and band structure calculations, leading to a three-order increase in JSC. The cosubstitution, following a charge compensation mechanism, decreases the lattice VO concentration significantly to retain the ferroelectric nature with enhanced polarization. It helps to achieve VOC (3-8 V) much larger than that of BiFeO3 (0.5-3 V). It is noteworthy that as Ca substitution maintains moderate crystallite size, the lattice VO concentration dominates GB-VO concentration. Notwithstanding, both lattice and GB-VO contribute to the increase in JSC; the former weakens ferroelectricity, and as a consequence, undesirably, VOC is lowered well below 0.5 V. Using optimum JSC and VOC, we demonstrate that the efficiency ∼0.22% can be achieved in solid-state BFO solar cells under AM 1.5 one Sun illumination.

Structural, Optical, and Multiferroic Properties of Yttrium (Y3+)-Substituted BiFeO3 Nanostructures

Nanoparticles of Bi1-xYxFeO3 (x = 0.0, 0.1, 0.15, 0.2) were synthesized by sol-gel pursued auto-combustion route. X-ray diffraction (XRD) pattern was recorded for analysis of the phase formation of pristine BiFeO3 (BFO) and Y3+-substituted samples. A systematic decrease in crystallite size with increasing concentration of Y3+ was observed by XRD and W-H plot. FESEM micrograph demonstrated clearly that the average grain size is decreased with increasing Y3+ ion concentration. Compositional analysis was carried out by EDS. Optical properties of the developed nanoparticles were examined by diffuse reflectance spectroscopy; it is observed that optical band gap decreases with increase in Y3+ ion concentration. Vibrating sample magnetometer (VSM) analysis revealed weak ferromagnetic behavior for pristine BFO. The ferromagnetic behavior has been enhanced with increasing concentration of Y3+ ions in BFO. Temperature dependence of dielectric constant shows an anomaly near the antiferromagnetic transition temperature in the developed materials that revealed the existence of magnetoelectric coupling in all the samples. Improved ferroelectric property has been observed by virtue of enhancement in the polarization of all substituted samples. Variation of electric field–guided strain with applied electric field has shown asymmetric behavior for samples x ≤ 0.15 and symmetric loop has been observed for x = 0.2 with the highest peak to peak strain value which makes it active material for electronic and magnetic devices.

Nd-Cr co-doped BiFeO3 thin films for photovoltaic devices with enhanced photovoltaic performance

BiFeO3 films and Nd-Cr co-doped BiFeO3 films were prepared by sol-gel method followed by spinning process on fluorine-doped tin oxide glass substrates. By testing the ultraviolet-visible absorption spectra, it was found that Nd-Cr co-doping will increase the light absorption rate of the film and reduce the optical band gap. The reduced bandgap can facilitate the transport of carriers. After Nd-Cr co-doping, the leakage current of the film is effectively reduced, which is near four orders of magnitude lower than the leakage current density of the pristine BiFeO3 film. The reduction of leakage current will enhance the ferroelectric polarization. The enhancement of ferroelectric polarization is more favorable for the separation of photogenerated carriers. Compared with the pristine BiFeO3 film, the short circuit photocurrent density, open circuit photovoltage and power conversion efficiency of Nd-Cr co-doped BiFeO3 film are all clearly improved. The Nd-Cr co-doped BiFeO3 films exhibited largely enhanced photovoltaic property, which favored the practical application of BiFeO3-based films in photovoltaic devices.

Structural and multiferroic properties of BiFeO3/MgLa0.025Fe1.975O4 nanocomposite synthesized by sol–gel auto combustion route

Nanocomposites of (1−x)BiFeO3(BFO)–xMgLa0.025Fe1.975O4(MLFO) (x = 0.0, 0.1, 0.2, 0.3 and 1.0) for enhanced multiferroic properties have been synthesized via sol–gel auto combustion route. Results of X-ray diffraction pattern, Field emission scanning electron microscopy and energy dispersive spectroscopy revealed the formation of composites and phase analysis for all the samples. Room temperature magnetic measurements (M–H curve) through vibrating sample magnetometer evidenced increasing trend in saturation magnetization (MS) from 0.23 to 5.28 emu/g for x = 0.0 to 0.3 samples, while smaller than MS value (17.06 emu/g) of MLFO nanoparticles. Antiferromagnetic transition or Neel temperature (TN1) for x = 0.0 and x = 0.3 samples were recorded by M–T plot (magnetization vs. temperature curve) and found to be 360 °C and 348 °C, respectively. Room temperature dielectric constant (er) and dielectric loss (tanδ) in the frequency range 100 Hz to 2 MHz were studied for x = 0.0 to 0.3 samples. Temperature-dependent dielectric constant for all the samples exhibited an anomaly near to the antiferromagnetic transition temperature of BFO. Improved ferroelectric property has been observed by virtue of enhancement in the polarization of composite samples. Electric field-guided strain as a function of the applied electric field has shown asymmetric behaviour for pristine BFO and symmetric loop has been observed for all the composite samples with increasing trend in highest peak-to-peak strain value (SP = 0.06 to 0.53% for x = 0.0 to 0.2 and 0.07 for x = 0.3) which makes these materials active for magnetoelectric devices.

Facile green synthesis of ytrium-doped BiFeO3 with highly efficient photocatalytic degradation towards methylene blue

Abstract Bismuth ferrite (BiFeO3) is considered as one of the most promising materials in the field of multiferroics with great potentials in photocatalysis due to their excellent properties of relatively small band gap, stable structures, and low cost. In this work, a facile green route was successfully used for the fabrication of high-purity yttrium-doped and undoped bismuth ferrite (BiFeO3) nanoparticles. κ-carrageenan seaweed was used as a biotemplate for the construction of the material. The obtained products were characterized and the photocatalytic effect of doped and undoped BiFeO3 were evaluated on the degradation of methylene blue (MB) under direct sunlight. The formed particles are in the range of 80–90 nm that exhibited morphology of rhombohedral perovskite structure as confirmed by FESEM and HRTEM analysis. Decreasing of band gap energy from 2.07 eV to 2.05 eV as the concentration of yttrium dopant increased significantly affected their photocatalytic behaviour. There was a remarkable improvement in the photocatalytic activity of 1% of yttrium-doped BiFeO3 towards the decomposition of methylene blue (MB) under direct sunlight irradiation. This was attributed to the strong absorption of visible light and the effective separation of photoinduced e− and h + pair, as compared to the pristine BiFeO3. In addition, the influence of operational parameters on the removal efficiency of MB, such as catalyst dosage and initial dye concentrations, was optimized as a function of time. The kinetics of the photocatalytic MB removal was later found to follow Langmuir Hinshelwood model.

BiFeO3/MoS2 nanocomposites with the synergistic effect between ≡MoVI/≡MoIV and ≡FeIII/≡FeII redox cycles for enhanced Fenton-like activity

BiFeO3/MoS2 nanocomposites with different composition ratios were synthesized under hydrothermal treatment and employed as heterogeneous Fenton-like catalysts. The nanocomposite sample with 80% MoS2 content exhibited the highest Fenton-like activity by degrading acid orange 7, which was 406.0 and 8.8 times higher than that of pristine BiFeO3 and MoS2, respectively. Instrumental characterizations including Raman and XPS were employed to deeply investigate the interfacial interaction between BiFeO3 and MoS2. The results indicated that the strong interfacial coupling of Bi-S bond was formed as a fast electron transfer channel where BiFeO3 could accept electrons from MoS2. A proposed mechanism suggested that the Fenton-like performance of BiFeO3/MoS2 was promoted by the synergistic effect between ≡MoVI/≡MoIV and ≡FeIII/≡FeII redox cycles.

Improved ferroelectric, magnetic and photovoltaic properties of Pr doped multiferroic bismuth ferrites for photovoltaic application

Multiferroic Bi1−xPrxFeO3 (x = 0.0, 0.05, 0.10, 0.15, 0.20) ceramic samples have been synthesized by sol-gel method. A detailed investigation has been made on structural, magnetic, electrical, optical and photovoltaic properties of Pr doped bismuth ferrites. A structural phase transition has been observed from (R3c) rhombohedral for pristine sample BiFeO3 to (Pnma phase) orthorhombic structure for Bi0.85Pr0.15FeO3 sample. A co-existence of (R3c) rhombohedral and (Pnma) orthorhombic phases were observed for 0.05 < x ≤ 0.15 samples. It is observed that the dielectric properties depend on Pr percentage in BFO. The values of dielectric constants for BFO, ε′ = 64.21 and ε′′ = 9.09 have been increased with Pr doping and maximum for Pr = 0.20 sample with values, ε′ = 111.79 and ε′′ = 55.79 at 100 Hz. The magnetization value 0.24 emu/g for BFO increases with Pr doping to maximum value 0.50 emu/g for Bi0.8Pr0.2FeO3 sample. The P-E loop study of the samples shows the modified ferroelectric behavior with Pr doping. The enhanced ferroelectric properties show increase in photocurrent upon illumination of light. Energy band gap value Eg = 2.44 eV for BFO, decreases with Pr doping and minimum value, Eg = 2.27 eV for Pr = 0.15 sample. The improved ferroelectric, magnetic and photovoltaic properties of Pr doped bismuth ferrites offer a new application in ferroelectric/multiferroic based photovoltaic devices.

Effect of La doping on the ferroelectric and optical properties of BiFeO3: a theoretical-experimental study

Much work has been done already on pure and doped BiFeO3 (BFO), however, renewed interest has emerged when considered as a viable photovoltaic material. It has been shown that, for this purpose, spontaneous polarization and energy gap are relevant physical quantities. In this theoretical-experimental work, we have studied the possibility of enhancing the spontaneous polarization and reducing the BFO bandgap by replacing 10% of the site A ions of the perovskite structure with La. The structural, electronic and optical properties of (Bi0.9La0.1)FeO3 were investigated using pristine BFO as a reference. A rhombohedral crystal structure was determined after La substitution and its corresponding bandgap of 2.49 eV was smaller than that of pure BFO. Theoretically, the spontaneous polarization (Ps) of the BFO increased with the incorporation of La up to a value of 103 μC cm−2, showing its effect on the ferroelectric properties. Moreover, the theoretical results and experimental measurements of the optical properties demonstrated the reduction of the optical gap.

Enhanced photovoltaic property based on reduced leakage current and band gap in Nd-doped BiFeO3 films

Nd-doped BiFeO3 films were successfully fabricated on FTO glass substrate via sol-gel and spin-coating methods. Both the short circuit photocurrent density and the open circuit photovoltage of Nd-doped BiFeO3 film are clearly improved compared with the pristine BiFeO3 film, leading to more than 8-fold enhancement in power conversion efficiency for Bi0.9Nd0.1FeO3. The enhanced photovoltaic property benefits from reduced bandgap and leakage current after Nd-doping. The leakage current density of the Bi0.9Nd0.1FeO3 film is two orders lower than that of the pristine BiFeO3 film, which is the lowest in the reported BiFeO3 films. Nd-doped BiFeO3 film also shows the better ferroelectric and dielectric properties, which favored the practical application of BiFeO3 in multifunctional devices such as nonvolatile ferroelectric memories, novel photovoltaic devices and high frequency electrical components.

Enhanced dielectric, magnetic and optical properties of Cr-doped BiFeO3 multiferroic nanoparticles synthesized by sol-gel route

Abstract Chromium-doped multiferroic bismuth ferrite BiFe1-xCrxO3 (x = 0.00, 0.01, 0.03, 0.05 and 0.07) nanoparticles (NPs) were synthesized by an ethylene glycol-based sol-gel technique and annealed at relatively low temperature of 550 °C. X-ray diffraction (XRD) confirmed the phase purity of pristine BiFeO3 and 1% Cr-doped BiFeO3 NPs. However, a slight impurity phase started to appear in 3% Cr-doped BFO which became significant in 5% and 7% Cr-doped samples. The crystallite sizes as determined by Scherrer equation were found to be 46 nm, 44 nm, 39 nm, 37 nm, and 34 nm respectively for pristine BiFeO3, BiFe0.99Cr0.01O3, BiFe0.97Cr0.03O3, BiFe0.95Cr0.05O3 and BiFe0.93Cr0.07O3 (referred to as BFO, BFC1O, BFC3O, BFC5O, and BFC7O respectively) NPs. In close agreement to this, the sizes determined by HRTEM was found to be 48 and 46 nm for BFO and BFC1O NPs, respectively. In the low frequency region, the dielectric constant (e′) shows a maximum decrease by 93% on 1% Cr-doping concomitant with 50% decrease in dielectric loss (tan δ) which indicates substantial reduction in leakage current density. Further, the pristine BFO shows a well-defined dielectric loss peak at 40 Hz (tan δ = 0.4) which shifts to 400 Hz for 1%, 3% and 7% Cr-doped NPs. Above 133 Hz, the 1%-Cr-doped NPs show greater loss as compared to pristine BFO NPs. The oxidation state of iron was found to be +3 by X-ray photoelectron spectroscopy (XPS), which was further corroborated by Mossbauer spectroscopy (MS). These nanocrystals with reduced leakage current and enhanced magnetic properties are well-suited for device applications.

Fabrication of dimension controlled BiFeO3 microcrystal

In this research, the effect of different KOH concentrations on the bismuth ferrite (BiFeO3) phase formation and microcrystal size was discussed. Pure phase BiFeO3 microcrystals were successfully synthesized through controlling different KOH concentrations during the hydrothermal process. The diverse sizes of pristine BiFeO3 microcrystals were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their photocatalytic activity was studied by photocatalytic degradation of methylene blue (MB) in aqueous solution under visible light irradiation. The results reveal that the composition and particle size of BiFeO3 microcrystals phase can be controlled with different mineralizer conditions. This work is able to provide a new perspective on the fabrication research of different dimension BiFeO3 microcrystals.

Tailoring the structural, optical and magnetic properties of BiFeO3 multiferroic nanoparticles by Ba, Cr co-doping

Phase pure BiFeO3 (BFO) and Bi0.98Ba0.02Fe1-xCrxO3 (x = 0.01, 0.02, 0.03, 0.04) nanoparticles were synthesized by a facile sol-gel route. X-ray diffraction data confirms rhombohedral R3c phase of BFO and Ba, Cr co-doped BFO nanoparticles with a slight distortion at higher dopant concentration. TEM images verified the higher crystallinity of the samples with a significant reduction in particle size (∼40 nm) with increasing Cr concentration. The band gap of pristine BFO nanoparticles was found to be 1.8 eV which increases remarkably to a maximum of 2.32 eV for Ba, Cr co-doped BFO nanoparticles. 57Fe Mössbauer spectroscopy confirmed that no mixed valance state of Fe was present in the Ba, Cr co-doped BFO nanoparticles. Hysteresis loops of all the samples revealed the weak ferromagnetic nature of the co-doped BFO nanoparticles. It was observed that the saturation magnetization increased by more than 3 times when Cr content was increased from 1% to 4%.

Phase transformation in crystal and magnetic structure and improved dielectric and magnetic properties of Ho substituted BiFeO3multiferroics

The changes in crystal and magnetic structure of BiFeO3 produced by partial substitution of Bi ions by Ho ions has been studied with powder X-ray diffraction, neutron powder diffraction, dielectric and magnetization techniques. The present study demonstrates that Bi1-xHoxFeO3(x = 0.05, 0.10, 0.15, &amp; 0.2) multiferroics shows change in crystal structure at x &amp;gt; 0.05. The sample with x = 0.05 exhibits rhombohedral structure (space group R3c), while the other three samples (x &amp;gt; 0.05) exhibit mixed phase with coexisting rhombohedral (R3c) and Orthorhombic (Pnma) structure. This change in the crystal structure is attributed to the distortion of FeO6 octahedra via substitution of Ho at phase boundaries. The magnetization studies indicate that doping of Ho in pristine BiFeO3 leads to enhancement in the ferromagnetic moment. We find that doping of Ho breaks the spin cycloid phase of BiFeO3 and creates a canted G-type antiferromagnetic structure in the hexagonal phase whereas the orthorhombic phase exhibits a collinear G-type AFM structure. The canting angle increases with increase in doping with Ho, leading to an enhancement in the ferromagnetic component in magnetization. Dielectric constant (ε′) and loss factor (tanδ) are measured in frequency range 1 kHz to 7 MHz and ε′ and tanδ show dispersion behaviour at low frequencies. The significant improvement in magnetization and dielectric properties is achieved by Ho substitution which in turn enhances the potential of BiFeO3 for multiferroics applications.

Effect of Ba and Ho co-doping on crystal structure, phase transformation, magnetic properties and dielectric properties of BiFeO3

Multiferroics having composition Bi0.80-xBa0.20HoxFeO3 (BBFO, BBHFO5, BBHFO10, BBHFO15 and BBHFO20 for x = 0.0, 0.05, 0.10, 0.15 and 0.20 respectively) were synthesized by method of solid state reaction. The crystal structure has been studied using X-ray diffraction technique. The X-ray patterns show enormous transform in crystal structure at concentration x = 0.20. The Rietveld refinement of XRD patterns indicates that at concentration x = 0.0 sample have rhombohedral structure with R3c space group while for the concentration x = 0.05, 0.10, 0.15 and 0.20, the mixed phase including rhombohedral R3c and triclinic P1 space groups were obtained with best fitting. This phase transformation in crystal structure is observed due to mismatching of ionic radii of doped ions and parent ions. Magnetic properties of all samples were carried out by using vibrating sample magnetometry. M-H hysteresis loops shows that with doping of Ba and Ho antiferromagnetic BiFeO3 (BFO) transforms into ferromagnetic. The dielectric and ferroelectric measurements were carried out which shows that dielectric constant, dielectric loss and ferroelectric properties are enhanced with co-doping of Ho in comparison of the pristine BFO due to structure deformation and decrease in oxygen vacancies with higher concentration of Ho. Significant improvement has been observed in dielectric constant and remnant magnetization values with increasing content of Ho and decrease in the dielectric loss.

Structural stability, enhanced magnetic, piezoelectric, and transport properties in (1-x)BiFeO3–(x)Ba0.70Sr0.30TiO3 nanoparticles

Multiferroic samples with composition (1-x)BiFeO3-(x)(Ba0.70Sr0.30)TiO3 (BFO-BST) were synthesized using a sol-gel route to study the effect of BST doping on structural, transport, and magnetic properties in BiFeO3 (BFO). X-ray diffraction studies with Rietveld analysis revealed that a phase transition occurred from rhombohedral (R3c) (0.0 ≤ × ≤ 0.15) to tetragonal (P4 mm) for x = 0.20 and nanocrystalline nature confirmed by transmission electron microscopy measurements. Piezoelectric properties improved as x increased from x = 0.0 (58 pC/N) to x = 0.20 (112 pC/N) increasing distortion in the crystal structure as evinced by Williamson-Hall analysis. Ferromagnetism was observed in doped BFO, different from the antiferromagnetic ordering in bulk BFO, indicating the noteworthy size effects and Fe-O-Fe bond angle variations in the magnetic ordering of BFO. An improvement in ferroelectric properties is observed with doping of BST compared to pristine BFO. Thermally activated conduction behavior occurred at low and high temperature regions as revealed by temperature dependent dc resistivity measurement. Effective improvements in dielectric response, meaning high dielectric constant with a low dielectric loss, were found in the doped samples.