Undoped BiFeO3 Research Articles

Investigations of the magnetic and dielectric behaviour of (Zr, Cu) co-doped BiFeO3-BaTiO3 composite

The multiferroic materials of BiFeO3 (BFO), Bi0.95Zr0.05FeO3 (BZFO) and Bi0.95Zr0.05Fe0.98Cu0.02O3 (BZFCO) synthesized by sol-gel route. The composites Bi0.95Zr0.05FeO3 (BZFO)-BaTiO3 (BTO) and Bi0.95Zr0.05Fe0.98Cu0.02O3 (BZFCO)—BaTiO3 (BTO) were prepared by solid-state reaction method. The x-ray diffraction reveals that the composite formation with proper interaction between BFO and BTO phases. Enhanced magnetic properties are noted for BZFCO-BTO composite as compared to single phase materials. The ME coefficient of BZFCO–BTO was found to be higher than the BZFO–BTO composite. The BZFCO-BTO composite has improved the dielectric properties of the single phase undoped and doped BFO. Detailed impedance spectroscopy analysis via Col-Col plot was used to determine the grain and grain boundary contribution on the resistive properties of the samples. The enhanced multiferroic properties of BZFCO-BTO composites compliment their potential application in energy storage devices and microelectrtonics.

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.

Performance Enhancement of Flexible Piezoelectric Nanogenerator via Doping and Rational 3D Structure Design For Self‐Powered Mechanosensational System

AbstractWith the rapid development of the Internet of things (IoT), flexible piezoelectric nanogenerators (PENG) have attracted extensive attention for harvesting environmental mechanical energy to power electronics and nanosystems. Herein, porous piezoelectric fillers with samarium/titanium‐doped BiFeO3 (BFO) are prepared by a freeze‐drying method, and then silicone rubber is filled into the microvoids of the piezoelectric ceramics, forming a unique structure based on silicone rubber matrix with uniformly distributed piezoelectric ceramic. When subjected to external force stimulation, compared with conventional piezocomposite films found on undoped BFO without a porous structure, the PENG possesses higher stress transfer ability and thus boosts output performance. The notable enhancement in the stress transfer ability and piezoelectric potential is proven by COMSOL simulations. The PENG can exhibit a maximum open‐circuit voltage (Voc) of 16 V and short‐circuit current (Isc) of 2.8 µA, which is 5.3 and 5.6 times higher than those of conventional piezocomposite films, respectively. The PENG can be used as a triggering signal to control the operation of fire extinguishers and household appliances. This work not only expands the application scope of lead‐free piezoelectric ceramic for energy harvesting, but also provides a novel solution for self‐powered mechanosensation and shows great potential application in IoT.

Change in structural, ferroelectric, and magnetic properties of bismuth ferrite induced by doping with gadolinium

Abstract Bismuth ferrite, BiFeO3, was doped with a wide range of concentrations (0–30%) of Gd in order to investigate structural, ferroelectric, and magnetic properties and their correlation. Powder samples of Bi1-xGdxFeO3 (x = 0.00–0.30) were prepared using the hydro-evaporation synthesis method. Sintering process at 870 °C for 6 h of as-prepared, Gd doped BiFeO3 powders resulted in ceramic samples with relative densities in the range of (74–86) %. XRD analysis revealed that Bi1-xGdxFeO3 samples (x = 0.00–0.09) crystallized in rhombohedral phase; Bi1-xGdxFeO3 samples (x = 0.10–0.20) contained both rhombohedral and orthorhombic phases, while Bi1-xGdxFeO3 (x = 0.30) sample contained only the orthorhombic phase. The structural parameters obtained after Rietveld refinement for single-phase Bi1-xGdxFeO3 ceramic samples and microstructure image analysis were correlated with the results of ferroelectric and magnetic measurements. Bi1-xGdxFeO3 (x = 0.0625, 0.075, 0.09) samples showed improved ferroelectric properties and reduced leakage current density in comparison with undoped BiFeO3. Gradual increase in Gd content in BiFeO3 led to enhanced magnetic responses and weak ferromagnetic behavior.

Enhanced multiferroïc properties in Bi(1-x)Y2x/3[Ti0.95(Yb0.5Nb0.5)0.05]xFe(1-x)O3 ceramics

Lead-free Bi(1-x)Y2x/3[Ti0.95(Yb0.5Nb0.5)0.05]xFe(1-x)O3 (BYTYNFO) (0 < x ≤ 0.3) ceramics were prepared by solid-state reaction. The effect of both substitutions in A and B sites on the structural, ferroelectric and magnetic properties of BiFeO3 was investigated. The Rietveld Refinement of X-ray diffraction data, recorded at room temperature, revealed rhombohedral R3c structure for x ≤ 0.15 compositions and a partial progressive structure transition to orthorhombic one (Pnma) for x = 0.2 and 0.3 compositions. The Mössbauer spectra demonstrated the progressive modulation of the magnetic spiral spin moments. The thermal analysis showed that as x increases the magnetic transition temperature TN deviated to room temperature compared to undoped BiFeO3 and the ferroelectric paraélectric TC temperature decreases. This deviation was discussed based on magnetic interaction and structure distortions. The obtained hysteresis loop (M versus H) and (P versus E) indicated that substitution led to an improvement of both magnetic and ferroelectric properties at room temperature. The sample with x = 0.3, presents a spontaneous polarization (Ps) of 7.74 μC/cm2. Magnetic measurements have been shown a weak ferromagnetism ordering and enhancement in magnetization which reached the highest remnant magnetization (Mr) values of 0,639 emμ/g for x = 0.2 composition. These results show that optimal BYTYNFO compositions are promising candidates for multifunctional devices.

Tailoring the multiferroic properties of BiFeO3 by co‐doping Er at Bi site with aliovalent Nb, Mn and Mo at Fe site

AbstractSingle phase multiferroic undoped BiFeO3 notoriously suffers due to the poor spin–charge coupling resulting in limitations to device applications. The present work focuses on the tailoring of its multiferroic and magnetoelectric coupling properties by synthesizing multiferroic Bi0.95Er0.05Fe0.98TM0.02O3 (TM = Nb, Mn and Mo) ceramics. The ferroelectric, magnetic, current leakage measurements and magnetoelectric effect were investigated. XRD along with the Reitveld refinement results confirms that all the samples possess perovskite based rhombohedral structure and reveals that doping of (Er, Nb), (Er, Mn) and (Er, Mo) induced the crystallographic distortion in the BFO lattice and hence induced a variation in the bond lengths and bond angle. Dual doping significantly enhanced the electrical, magnetic properties and magnetoelectric coupling as compared to BiFeO3. Doping has lowered the leakage current by three to four orders compared to BFO. The lattice distortion, reduced leakage current and destruction of spin–cycloidal structure could be the origin for these improved features. The (Er, Nb) doped BiFeO3 yields enhanced ferroelectric character with the maximum polarization value of 0.46 µC/cm2, maximum ME coupling of 0.22 mV/cm at a magnetic field of 130 G, an improved magnetization with a remanance value of 0.0903 emu/g and the lowest leakage current density.

Effects of Gd and Cr co-doping on structural and magnetic properties of BiFeO3 nanoparticles

In this work, Gd and Cr co-doped Bi0.95Gd0.05Fe1−xCrxO3 (x = 0–0.08) functional ceramics were synthesized by chemical solution deposition technique (CDS). The synthesized samples were annealed at different temperatures between 400 °C–700 °C. The x-ray diffraction (XRD) study revealed a partial phase evolution from R3c (rhombohedral) crystal structure to pna21 crystal structure (orthorhombic) with Gd doping which further enhanced with increasing Cr co-doping. XRD analysis has shown a significant reduction in crystallite size to 25 nm from 68 nm of un-doped BiFeO3. Field Emission Scanning Electron Microscopy (FESEM) exhibited more uniform nanoparticles due to doping effects and the average size of particle was found to be higher compared to that obtained from XRD results. The magnetic measurement showed a significant improvement in ferromagnetic properties of the synthesized samples, in particular, an enhanced magnetization was obtained for 5 at% Gd + 6 at% Cr co-doped multiferroics compared to un-doped one. In addition, a prominent exchange anisotropy effect was observed from unsymmetrical M-H loops in all the samples at room temperature signifying promising practical applications.

Electric current activated sintering (ECAS) of undoped and titanium-doped BiFeO3 bulk ceramics with homogeneous microstructure

BiFeO3 ceramics have been consolidated applying an electric current activated/assisted sintering (ECAS) methodology under different electrical conditions. DC experiments produce a flash sintering regime by which the bulk cylindrical specimens densify in a few seconds; however, this goes together with a strong localization of the current flow within the material, leading to a dramatic lack of microstructural and compositional homogeneity. The situation changes under the alternate field; a more gradual FAST (Field Assisted Sintering) event is produced which allows the attainment of an exceptional microstructural homogeneity through the whole sintered compacts. Upon Ti-doping the overall diffusivity of the system is delayed but the AC conditions again yield a remarkable microstructural homogeneity in the consolidated material, this time even at the nanoscale level. Accordingly, bulk BiFeO3 ceramics with homogeneous micro-nanostructure can be successfully prepared by an ECAS methodology and at lower temperatures and much shorter times than by conventional solid-state sintering.

Multiferroism and magnetoelectric coupling in single-phase Yb and X (X = Nb, Mn, Mo) co-doped BiFeO3 ceramics

A series of Yb and X co-doped BiFeO3 (X = Nb, Mn, Mo) and undoped BiFeO3 polycrystalline ceramics were prepared by sol-gel method. The X-ray diffraction pattern confirmed the rhombohedral perovskite structure for all the ceramics. Reitveld refinement results bring out the impact of doping on the structural distortion. The Transmission Electron Micrograph observation reveals the nanostructure of the doped samples. Well saturated ferromagnetic hysteresis curves were obtained for the doped samples in contrary to undoped BiFeO3 and this is attributed to the distortion of spin spiral structure. The doped ceramics exhibited improved ferroelectric parameters and very low leakage current density of the order of 10−9 to 10−7 A/cm2, which is remarkably lower than that of undoped BFO. Remarkable dielectric properties were exhibited for the doped samples. An abrupt noticeable enhancement of magetoelectric coupling for the doped samples in comparison with the undoped BiFeO3 has been demonstrated in our work.

Effects of Gd and Cr co-doping on multiferroic properties of Bi0.9Gd0.1Fe(1-x)CrxO3 (x = 0−0.08)

Gd and Cr co-doped Bi0.9Gd0.1Fe(1 − x)CrxO3 (x = 0 − 0.08) nanoparticles were synthesized via sol-gel method. Precursor salts of bismuth, iron, gadolinium and chromium were used as starting raw materials. Obtained nanoparticles were annealed at various temperatures between 400 − 700 °C. Optimal properties were found to display at 600 °C. X-ray diffraction (XRD) patterns revealed that the partial substitution of Bi3+ by Gd ions and Fe3+ by Cr ions in BiFeO3 (BFO) resulted in evolution of phase transition from rhombohedral to orthorhombic structure. The average crystallite size was found to vary from 16 to 68 nm depending on doping level. The field emission scanning electron micrographs demonstrated a distinct morphology of spherical and nano-sized particles. Ferroelectric measurements showed a substantial improvement in polarization in doped BFO under an applied field of ± 30 kV/cm. Magnetic properties measured at room temperature showed enhanced ferromagnetic characteristics with increasing doping level of Cr up to 6 % (at.) compared to that of un-doped BFO. An asymmetric shift both in the field and magnetization axes of M-H loops was also observed.

Hydrothermal synthesis of pure and Sb-doped BiFeO3 with the typical hysteresis loops of ideal ferroelectrics

BiFeO3 (BFO) samples with nearly perfect ferroelectric hysteresis loops were synthesized from chemical solution via hydrothermal route at 200 °C. However, for many applications, ceramic samples of reasonable bulk density (>80%) have to be sintered at temperature over 700 °C, which in this case results in a significant reduction in resistivity due to increased amounts of Fe2+. Interestingly, doping of a few percent Sb minimized such a problem and the sintered Sb:BFO ceramics retained a similarly high resistivity as samples cold-pressed from the chemical-solution synthesized powders. However, for cold-pressed samples, Sb:BFO actually had higher conductivity than undoped BFO. Temperature-dependent conductivity showed that cold-pressed samples of both undoped and Sb doped BFO had the similar activation energy of 1.0 eV, typical for electrons trapped in oxygen vacancies. After sintering, the activation energy of Sb:BFO remained almost unchanged, but the activation energy of undoped BFO changed to 0.4 eV, which is associated to electron hopping between Fe2+/Fe3+. X-ray photoelectron spectroscopy (XPS) showed a significant increase in Fe2+/Fe3+ ratio from 6.6/93.4 to 25.7/74.3 in undoped BFO after sintering, while for 1% Sb doped BFO the increase was much milder from 10.9/89.1 to 14.1/85.9. XPS also showed that Sb had single +3 oxidation state before sintering, but after sintering a fairly large portion of Sb5+ occurred. So, charge compensation for oxygen vacancies in undoped BFO was achieved dominantly by reduction of Fe3+ to Fe2+, while in Sb:BFO it was achieved more by cation vacancies.

Low-spin Co3+ make great contributions to the magnetism of BiFeO3

Various spin states of Co3+ were tested in Co-doped BiFeO3 (BFO) through first-principle method, aimed to reveal the role of spin state transition of Co3+ in developing ferrimagnetism. It is found that low-spin (LS) Co3+ contributed much more to resultant magnetic moment than high-spin (HS) Co3+ (~ 3.914 µB). To explore the electronic origins of the enhanced magnetism, a more detailed analysis is carried out including electronic configuration of HS and LS Co3+ as well as Co–O hybridization. It is demonstrated that the LS Co3+ which is nonmagnetic could destroy the cycloid–dal spin structure of BFO. Moreover, LS Co3+ has vacant 3d orbitals so that the p–d covalency is enhanced and the local ferrimagnetism is improved. The structural origin of the Co3+ spin-state transition is ascribed to the distortion of CoO6 octahedra. To explore the influence of Co doping experimentally, the 8% Co-doped and un-doped BFO powders were prepared. The Hysteresis loops indicated that the substitution of Co led to a slight increase of magnetization, i.e. HS Co3+ made limited contribution to the magnetism of BFO.

Structural, surface morphology, dielectric and magnetic properties of holmium doped BiFeO3 thin films prepared by pulsed laser deposition

In this work, Bi1-xHoxFeO3 (with x = 0, 0.05, 0.10, 0.15 and 0.20) thin films were successfully grown on Si (100) substrates using pulsed laser deposition and the effect of Ho doping on the crystal structure, dielectric and magnetic properties were studied. X-ray diffraction studies on undoped BiFeO3 confirmed the presence of a rhombohedral phase with crystallite sizes in the 14–24 nm range. The surface morphology and microstructure of the thin films were analysed by field emission scanning electron microscopy and atomic force microscopy. The results reveal that the grain size decreases as the Ho doping concentration increases. X-ray photoemission spectroscopy was used to identify the chemical bonding, valance band and core levels of Ho doped BiFeO3 thin films. Dielectric constant and loss in Ho doped samples has been measured using a vector network analyzer and shows good dielectric behaviour compared to undoped BiFeO3. A vibrating sample magnetometer was used to investigate the magnetic properties for Ho doping with concentrations of x ≥ 0.15. In comparison to undoped BiFeO3, the doped films exhibited larger remanence and saturation magnetization. The enhancement of these properties due to Ho doping is discussed along with their relevance in designing multiferroic materials based on Bi1-xHoxFeO3 films for magnetic field sensors, multiple-state memories and spintronic elements.

Enhanced heterogeneous Fenton-like activity by Cu-doped BiFeO3 perovskite for degradation of organic pollutants

Heterogeneous Fenton-like reaction has been extensively investigated to eliminate refractory organic contaminants in wastewater, but it usually shows low catalytic performance due to difficulty in reduction from Fe(III) to Fe(II). In this study, enhanced catalytic efficiency was obtained by employing Cu-doped BiFeO3 as heterogeneous Fenton-like catalysts, which exhibited higher catalytic performance toward the activation of H2O2 for phenol degradation than un-doped BiFeO3. BiFe0.8Cu0.2O3 displayed the best performance, which yielded 91% removal of phenol (10 mg L–1) in 120 min. The pseudo first-order kinetic rate constant of phenol degradation in BiFe0.8Cu0.2O3 catalyzed heterogeneous Fenton-like reaction was 5 times higher than those of traditional heterogeneous Fenton-like catalysts, such as Fe3O4 and goethite. The phenol degradation efficiency could still reach 83% after 4 cycles, which implied the good stability of BiFe0.8Cu0.2O3. The high catalytic activity of BiFe0.8Cu0.2O3 was attributed to the fact that the doping Cu into BiFeO3 could promote the generation of Fe(II) in the catalyst and then facilitate the activation of H2O2 to degrade the organic pollutants.

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

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

Structural transitions and multiferroic properties of high Ni-doped BiFeO3

Nickel doped bismuth ferrite powders, BiFe1−x NixO3 (0 ≤ x ≤ 0.5), were synthesized by high-energy ball milling followed by an annealing at 700 °C. A detailed study about the substitution of Fe3+ by Ni2+ on the crystal structure and multiferroic properties is presented. The X-ray diffraction patterns reveal the formation of rhombohedral structure with small amounts of Bi2Fe4O9 as a secondary phase for x < 0.1. Also it is inferred the stabilization of a Bi25FeO40, sillenite phase, as the amount of Ni2+ substitution increases, reaching up 95.23% of sillenite for x = 0.5. The magnetic behavior indicates the frustration of the G-antiferromagnetic order typical of the un-doped BiFeO3, caused by the presence of small amounts of Ni2+ (x < 0.1) on the structure. The DC conductivity exhibited a little increment with increasing Ni content (up to x = 0.1). Although the conductivity increases, for nickel concentrations of 0.2–0.5, the bismuth ferrites doped with nickel retain their property of being an electrical insulating material. Behavior modifications of electrical conductivity, permittivity and dielectric loss versus frequency are related with crystal structure transformations, when nickel concentration is increased.

The Effect of Ba Doping on the Structural, Optical, Magnetic, and Dielectric Properties of BiFeO3 Nanoparticles

Nanoparticles (Nps) of Ba (0, 1 to 5 at.%)-doped BiFeO3 were synthesized by a sol-gel route at 100 °C using tartaric acid as a chelating agent. The obtained results were studied by using XRD, SEM with EDAX, TEM, UV-vis diffusion reflectance spectra, VSM, and impedance analyzer. EDAX spectra confirmed the presence of Bi, Ba, and Fe in the samples. X-ray diffraction studies showed that BiFeO3 and Bi1−xBaxFeO3 samples exhibited the expected rhombohedral perovskite structure up to a Ba concentration of 3%, whereas 4 and 5% of Ba concentration exhibited the tetragonal phase. TEM studies indicate the particle sizes in the range of 08–28 nm. Reflectance spectra measurements showed a decrease in band gap with increasing Ba concentration. Magnetic properties indicated that the undoped BiFeO3 and Ba-doped BiFeO3 samples were ferromagnetic at room temperature. The dielectric constant (e′) and loss (e″) show large dispersion behavior. The dielectric constant increases with an increase of dopant concentration, but a very high value of the dielectric constant was noticed for x = 0.05.

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

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

The impact of Yb and Co on structural, magnetic, electrical and photocatalytic behavior of nanocrystalline multiferroic BiFeO3 particles

The nanocrystalline particles of BiFO3,co-doped with ytterbium and cobalt Bi1−xYbxCoyFe1−yO3 (BYCFO) were fabricated via micro-emulsion method using cetyltrimethyl ammonium bromide (CTAB) as a surfactant. The dopant contents were kept x = 0.00, 0.025, 0.05, 0.075, 0.1, 0.125 and y = 0.00, 0.05, 0.1, 0.15, 0.2, 0.25 for six different compositions. The BYCFO-nanoparticles were investigated for structure, electric, dielectric, magnetic and photocatalytic properties. The X-ray diffraction (XRD) analysis confirmed the normal growth habitat Rhombohedral (R3c) phase on inclusion of ytterbium and cobalt ions as it is observed in undoped BiFeO3 multiferroic. However further doping of Yb+3 and Co+3 ions (x = 0.125, y = 0.25) resulted in some extra peaks, that is attributed to the formation of extra phase. The vibrating sample magnetometer recorded saturated magnetization (Ms) 0.385emu/g with remanent magnetization (Mr) 0.13emu/g for a coercivity of 405Oe which is higher than the undoped BiFeO3. The substitution of Yb+3 and Co+3 ions improved the canting angle and optimally aligned the sub lattices in ferromagnetic order. The grain size was found in the range of 20–24nm which is less than spiral spin modulation (≈ 62nm). The entire dielectric parameters showed smooth decreasing trend in low range frequency but at higher frequency (1.98GHz) resonance peaks appeared in the spectra. The insulating character was also enhanced up to 16.42 × 1010Ωcm−1, with increase in doping concentrations. The optical band gap was measured 1.5eV which was lower than the undoped BiFeO3 (2.15eV). The photocatalytic performance of co doped ceramic (Bi0.875Yb0.125Co0.25Fe0.75O3) was monitored using the textile dye Congo red. Approximately 28% of initial concentration (0.5ppm) was degraded by 200mg of ceramics in 42min under visible light irradiation. Being magnetic in nature, the Bi1−xYbxCoyFe1−yO3 particles could be separated by conventional magnetic bar.

Temperature-dependent phase transition and comparative investigation on enhanced magnetic and optical properties between sillenite and perovskite bismuth ferrite-rGO nanocomposites

The manuscript reports the synthesis as well as a comparative investigation of the structural, magnetic, and optical properties between sillenite and perovskite type bismuth ferrite-reduced graphene oxide nanocomposites. Graphite oxide is prepared using the modified Hummers' method, followed by hydrothermal synthesis of bismuth ferrite-reduced graphene oxide nanocomposites at different reaction temperatures. The X-ray diffraction measurements confirm the formation of perovskite type BiFeO3-rGO nanocomposites at a reaction temperature of 200 °C. This is the lowest temperature to obtain perovskite type BiFeO3-rGO nanocomposites under the reaction procedure adopted, however, a structural transition to sillenite type Bi25FeO40-rGO is observed at 180 °C. The FESEM images demonstrate that the particle size of the perovskite nanocomposite is 25–60 nm, and for the sillenite phase nanocomposite it is 10–30 nm. The as-synthesized nanocomposites exhibit significantly enhanced saturation magnetization over pure BiFeO3 nanoparticles, with the sillenite Bi25FeO40-rGO nanocomposite having higher saturation magnetization than perovskite BiFeO3-rGO. The optical characteristics of the as-synthesized nanocomposites demonstrate considerably higher absorbance in the visible range with significantly lower band gap in comparison to undoped BiFeO3. Again, the sillenite Bi25FeO40-rGO nanocomposite is shown to have a lower band gap compared to the perovskite counterpart. Our investigation provides a means of selective phase formation as desired between sillenite Bi25FeO40-rGO and perovskite BiFeO3-rGO by controlling the hydrothermal reaction temperature. The outcome of our investigation suggests that the formation of nanocomposite of sillenite bismuth ferrite with reduced graphene oxide is promising to improve the magnetic and optical properties for potential technological applications.