Papers by Keyword: BiFeO₃

Abstract: A single layer of BiFeO₃ (BFO)/epoxy resin composite with thickness of 3 mm was fabricated by polymerized 70 wt% of sintered BFO as fillers and 30 wt% of epoxy resin polymer as matrix. The electromagnetic and the microwave absorption properties of BFO/epoxy resin composite were reported. The reflection loss (RL) of the same composite sample was measured by two different techniques of measurement, S_11a parameter (without metal backed reflector) and S_11b parameter (with metal backed reflector) in the range of 8-18 GHz using a network analyzer. Minimum RL (RL_min) from S_11b parameter for BFO/epoxy resin composite with metal backed is lower than the RL_min from S_11a composite without metal backed reflector. In details, the results showed BFO/epoxy resin composite with metal backed can achieve a strong absorption with RL_min of -40.5 dB over a 1.31 GHz bandwidth.

Abstract: It is expected that BiFeO₃-based materials will have both ferroelectricity and ferromagnetism. (1-y)BiFe_(1-x)Mn_xO₃-yBaTiO₃ system was prepared using solid state reaction method. The goal of this study is to uncover the impacts of Mn doping and BaTiO₃ content on the crystal structure, magnetism and ferroelectric properties. By forming a solid solution with BaTiO₃, stable perovskite BiFeO₃ was achieved. The rhombohedrally distorted (1-y)BiFe_(1-x)Mn_xO₃-yBaTiO₃ showed weak ferromagnetism due to the composition of BaTiO₃ and the doping of Mn ion. 0.8BiFe_0.9Mn_0.1O₃-0.2BaTiO₃ and 0.7BiFe_0.9Mn_0.1O₃-0.3BaTiO₃ ceramics exhibited typical P-E hysteresis loops.

Abstract: Citric acid assisted auto combustion method was used in the synthesis of BiFeO₃ nanoparticles. The synthesized nanoparticles were characterised using X-ray powder diffraction, Scanning electron Microscope, BET surface area analysis, UV-Visible Diffuse Reflectance Spectrometer and Vibratory Sample Magnetometer. The photocatalytic behaviour of the BFO nanoparticles has been studied by the degradation of the direct blue dye. It is observed that BFO shows a good photocatalytic degradation of dye in the visible light irradiation. The effect of pH, catalyst quantity has been studied. The optimum condition is identified as pH 2 and 150mg of the photocatalyst in 10ppm of the dye solution. The magnetic property of BiFeO₃at room temperature helps in the efficient removal of them from the treated dye solution. The ability of BiFeO₃ nanoparticles to absorb the solar energy and using it for the treatment of water gives it an upper hand over other photo catalysts like Titanium Oxide (TiO₂) and Zinc Oxide (ZnO).

Abstract: In order to improve the structural and ferromagnetic property of BiFeO₃, the effects of Ho³⁺ doping is systematically investigated. Pure BiFeO₃ and Ho-doped BiFeO₃ thin films are fabricated by sol-gel method, and the phase structure, morphology, crystalline structure, ferromagnetic are characterized by XRD, SEM, Raman spectra and VSM, respectively. The XRD patterns of the samples indicate that all the compounds crystallize in rhombohedral distorted perovskite structure with space group R₃c and the Ho substitution can suppress the intrinsic formation of the miscellaneous phase. The SEM proves that along with the increasing of Ho concentration, the surface roughness of BiFeO₃ is decreased due to the reduction of defects in the preparation. From the Raman spectroscopy, it is found that the peak intensity of 8 modes in Bi_1-xHo_xFeO₃ are increased and the modes shift to higher wave number. Besides, the VSM results show that the ferromagnetic of the samples is enhanced with increasing of Ho concentration. When x=0.1, Ms is improved to be 4.8emu/g. The results can prove that the Ho³⁺ doping can reduce the volatilization of Bi³⁺, decrease the concentration of oxygen vacancies and improve the room-temperature ferromagnetic of BiFeO_3.

Abstract: Pure BiFeO₃ (BFO), Ca-doped and Eu/Ca-codoped BFO nanoparticles were prepared by using a sol–gel method. The effects of Eu/Ca-codoped on the structural, magnetic and ferroelectric properties of the samples were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the codoped samples. Co-doped samples were obtained with the best ferromagnetic properties, with the largest remaining magnetization Mr = 0.20 emμ/g. The structure transition may be the main cause for the origin of improved magnetic properties, which destroys the space modulated spin structure of BFO and releases the locked magnetic. In addition, the doping of Eu into BFO can reduce the leakage current and enhance the ferroelectric properties.

Abstract: The photovoltaic effect in Ag/Bi_0.9La_0.1FeO₃/La_0.7Sr_0.3MnO₃ heterostructures was investigated and the short circuit photocurrent was found to be strongly dependent on the polarization orientation and oxygen vacancies (V_Os) distribution. The photocurrent direction was switched accompanying polarization switching. Besides, according to manipulate the V_Os accumulated at either the Ag/Bi_0.9La_0.1FeO₃ or the Bi_0.9La_0.1FeO₃/La_0.7Sr_0.3MnO₃ interface by electric pulses, obvious enhancement of photovoltaic effects was obtained. These results can be explained well using the concepts of drift current and diffusion current controlled by the combination of oxygen vacancies and polarization. This work provides deep insights into the nature of photovoltaic effects in ferroelectric films, and will facilitate the advanced design devices combining spintronic, electronic, and optical functionalities.

Abstract: To investigate the epitaxial strain effect on local electronic structure of FeO₆ octahedron of BiFeO₃ epitaxial film, polarization-dependent Fe L₂₃-edge x-ray absorption spectroscopy studies were performed on both tetragonal (T)-like BFO/LAO and rhombohedral (R)-like BFO/STO epitaxial films. Charge transfer multiplet theory based fittings were also performed to reveal the local electronic structure difference. Due to dramatic structural difference caused by epitaxial strain between these two samples, significant electronic structure differences were observed between these two specimens. For BFO/LAO, anisotropic electronic structure appears in vertically-elongated FeO₆ octahedron and an additional shift of Fe ion off the central position is suggested. For BFO/STO, electronic structure is almost isotropic.

Abstract: Bi_0.9Ba_0.1Fe_0.95O₃ and Bi_0.9Ba_0.1Fe_xTi_0.05O₃ (x=0.95, 0.925, 0.90) ceramics were prepared through conventional solid state reactions. X-ray diffraction analyses indicated that a high content of perovskite phase was obtained for all the four compositions. While the three (Ba,Ti)-codoped compositions all showed a higher resistivity than Bi_0.9Ba_0.1Fe_0.95O₃, and Bi_0.9Ba_0.1Fe_0.925Ti_0.05O₃ had the best electrical and dielectric properties among the three (Ba,Ti)-codoped compositions, including the largest dielectric constant, the smallest dielectric loss at low frequency range, and the highest electrical resistivity. Magnetic hysteresis loop measurement revealed that the four compositions had similarly enhanced magnetic properties. It is concluded that much attention should be paid to fine composition adjustment when multiple elements are co-doped to BiFeO₃ system.

Abstract: (Bi_1-xSm_x)(Fe_0.95Mn_0.05)O₃ (x=0.00, 0.03 and 0.06) thin films were deposited on the quartz substrates by sol-gel technique. The results of X-ray diffraction patterns indicated all thin films had rhombohedral perovskite structure. Moreover, the Sm and Mn co-doping at A-and B-site of BiFeO₃ resulted in the structural distortion. Scanning electron microscope measurements exhibited that the uniform surface morphology could be obtained by co-doping and the average grain size of the films decreased with increasing Sm content. Furthermore, the fundamental absorption edges of xBSFMO films showed a blue shift with the increase of Sm content which can be observed in transmittance spectra. The optical band gap of the thin films for x= 0.00, 0.03 and 0.06 can be expressed by (0.84x+2.62) eV, which is due to the Burstein-Moss effect.

Abstract: BiFeO₃ films undoped and doped with Ba and/or Ti have been fabricated through Metal-Organic Chemical Vapor Deposition (MOCVD) on SrTiO₃ (100), SrTiO₃:Nb (100) and YSZ (100) substrates. Films have been deposited using a multi-metal source, consisting of the Bi (phenyl)₃, Fe (tmhd)₃, Ba (hfa)₂•tetraglyme and Ti (tmhd)₂(O-iPr)₂ (phenyl= -C₆H₅, H-tmhd=2,2,6,6-tetramethyl-3,5-heptandione; O-iPr= iso-propoxide; H-hfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme = CH₃O(CH₂CH₂O)₄CH₃) precursor mixture. The structural and morphological characterization of films has been carried out using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Chemical compositional studies have been performed by energy dispersive X-ray (EDX) analysis. Structural and morphological characterizations point to the formation of crystalline phases and homogeneous surfaces for both undoped and doped BiFeO₃ films. Piezoresponse force microscopy (PFM) and piezoresponce force spectroscopy (PFS) have been applied to study the piezoelectric and ferroelectric properties of the films.