A comparative study of structural,electrical and magnetic properties rare-earth (Dy and Nd)-modified BiFeO3

The polycrystalline samples of BiFeO₃ (BFO) and rare earth-modified bismuth iron oxide, Bi_0.95R_0.25FeO₃ (R = Nd, Dy) (BNFO, BDFO) are prepared by a standard high-temperature solid-state reaction technique. A preliminary x-ray structural analysis is carried out to examine the structural deformation and stability of rare earth-modified BFO. Room temperature surface morphologies and textures of the samples are recorded by a scanning electron microscope, which reveals the uniform distribution of the plate-and rod-shaped grains. Studies of dielectric and electric properties in a wide frequency (1 kHz–1 MHz) and temperature (30–400 °C) ranges using complex impedance spectroscopic method have provided many new results. The dielectric constant is found to be increases, and the tangent loss decreases as compared to BFO. The electrical polarizations (spontaneous and remnant) is found to be enhanced on rare-earth substitutions. Studies of ac conductivity suggest that the samples obey Jonscher’s universal power law. The enhancement of magnetization was observed in rare-earth doped samples compared to pure BFO.     

Enhancement of dielectric and electrical properties of NaNbO3-modified BiFeO3

Solid solutions of BiFeO₃ (BFO) and NaNbO₃ [i.e., (Bi_1?xNa_x) (Fe_1?xNb_x)O₃] for x = 0.1, 0.2, 0.3 were prepared by a mixed-oxide method. X-ray diffraction analysis confirms the formation of a single-phase system within a certain limit of x, and indicates that with increase in concentration of NaNbO₃ there is structural transformation of BFO from the rhombohedral to the tetragonal phase. The dielectric constant and loss-tangent of samples increase with rise in temperature. It is found that with increase of concentration of NaNbO₃ in the solid solution, tangent loss of BFO is greatly reduced that can be useful for some industrial applications. The appearance of hysteresis loops of the samples at room temperature confirms the ferroelectric properties of the materials. As the electrical conductivity of the above system increases with rise in temperature, it follows the Arrhenius relation. The frequency and temperature dependence of conductivity of the above system obeys Joncher’s universal power law. Some voltage is induced with the application of magnetic field confirming the existence of multiferroics properties in the materials. Leakage current reduces with increase in content of NaNbO₃ in the solid-solutions.     

Role of Bi-excess on structural,electrical, optical,and magnetic properties BiFeO3 nanoparticles

Journal of Materials Science: Materials in Electronics - The influence of Bi content on structural, optical, and multiferroic properties of BiFeO3 has been studied. The nanoparticles of BiFeO3 with...     

A comparative study of the effects of rare-earth oxides on the physical,optical, electrical and structural properties of vanadium phosphate glasses

The physical parameters such as density, X-ray diffraction, infra-red absorption spectra and optical absorption measurements are discussed with respect to all compositions. The d.c. conductivity was measured for semi-conducting vanadium phosphate glasses containing 5 mol% rare-earth oxides. The conductivity of vanadium phosphate glasses is slightly higher than the corresponding compositions with rare-earth oxides. The heat treatment in the range 300 to 500° C caused progressive microstructural changes which dramatically affected the electronic conductivity () and the activation energy for conduction (W). It was also found that the incorporation of rare-earth oxides did not affect the limits of the ultra-violet absorption edge of the base glass.     

Ferroelectric and magnetic properties of multiferroic BiFeO(3)-based composite films

BiFeO(3)-based composite films were fabricated onto the Pt/Ti/SiO(2)/Si(100) substrates by a chemical solution deposition (CSD) method using the precursor solutions with various excess iron composition followed by annealing at 923 K for 30 minutes under oxygen gas flow. Coexistence of spontaneous magnetization and remanent polarization could be obtained in the BiFeO(3)-based composite films with high excess iron composition. The remanent magnetization of almost 20 emu/cm(3) and the magnetic coercive field of 1.5 kOe were obtained at the iron composition ratio of Fe/Bi = 1.25. In this specimen, the remanent polarization at 90 K was approximately 10 microC/cm(2) at the electric field of 1500 kV/cm. Structural analysis suggested that the remanent polarization has a possibility to increase by suppressing the formation of the secondary phases of Bi(2)Fe(4)O(9) and alpha-Fe(2)O(3), these are the nonferroelectric material as well as antiferromagnetic phase.     

Sol-gel synthesis and characterisation of (Nd,Cr) co-doped BiFeO3 nanoparticles

Bi_0.95Nd_0.05Fe_1–xCr_xO₃ (x = 0, 0.01, 0.03, 0.05) samples are synthesised by the sol-gel method. The variation in structure, magnetisation, electrical and photocatalytic properties by Cr doping at Fe site in Bi_0.95Nd_0.05FeO₃ samples is analysed. X-ray diffraction pattern confirms the formation of rhombohedral structure in all the samples. The crystallite size is calculated using the Scherrer relation and found to be in nanometre range. Kubelka-Munk theory is used to determine the direct band gap of the samples from reflectance spectra. The saturation magnetisation is found to enhance the concentration of chromium. Arrott-Belov-Kouvel plot confirms the ferromagnetic nature in the samples. The leakage mechanisms are studied to understand the influence of Cr concentration on the BFO. A good correlation exists between the leakage current and ferroelectric behaviour. Photocatalytic tests show degradation of methylene blue dye in the presence of H₂O₂. A drastic decrease in photocatalytic activity is observed with the concentration of Cr.     

Influence of Al doping in LaCoO3 on structural,electrical and magnetic properties

We report investigations on polycrystalline LaCo_1?x Al _x O₃ (x = 0–0.9) bulk samples. The solid state synthesized samples showed a coexistence of rhombohedral and monoclinic phases in the intermediate concentrations (0.2 ≤ x ≤ 0.5) and pure rhombohedral phase otherwise. The observed effect of Al doping on dc transport has been analysed on the basis of small polaron hopping mechanism. The magnetisation results presented give evidence of weak ferromagnetism and anomalous temperature dependence of coercivity which we associate to the canting of the localised high-spin Co(III) and anti-symmetric exchange interactions at low temperatures.     

Magnetic and electrical properties of multiferroic BiFeO3, its synthesis and applications

Major ways to improve the magnetic and electrical properties of promising multiferroic BiFeO₃ and optimize its synthesis have been studied, and its applications in spintronics, photonics, and magnonics have been discussed.     

Structural,dielectric and electrical properties of Al+3-modified PLZT ceramics

Polycrystalline samples of [Pb_0.92(La_1−zAl_z)_0.08][Zr_0.60Ti_0.40]_0.98O₃ (z=0.0, 0.3, 0.6, 0.9, 1.0) were prepared by a high-temperature solid-state reaction technique. Preliminary X-ray study at room temperature shows the formation of single-phase compounds in the tetragonal crystal system. Scanning electron microscopy (SEM) study was employed to observe the microstructure and distributions of grains of the sintered ceramics. Detailed studies of dielectric constant (ϵ) and tangent loss (tanδ) of the compounds as a function of frequency (100 Hz–1 MHz) at different temperature (30–400 °C) show that the compounds have a diffuse ferroelectric phase transition. As we increase z, transition temperature shifts towards higher temperature side. The dc conductivity of the material (as evaluated from the impedance analysis) has been observed to be ∼10⁻⁸ S cm⁻¹ at room temperature (RT) and ∼10⁻⁴ S cm⁻¹ at 550 °C which has indicated a typical semiconductor like behavior with negative temperature coefficient of resistance (NTCR).     

Dependence of ferroelectric and magnetic properties on measuring temperatures for polycrystalline BiFeO(3) films

A multiferroic BiFeO(3) film was fabricated on a Pt/Ti/SiO(3)/Si(100) substrate by a chemical solution deposition (CSD) method, and this was followed by postdeposition annealing at 923 K for 10 min in air. X-ray diffraction analysis indicated the formation of the polycrystalline single phase of the BiFeO(3) film. A high remanent polarization of 89 microC/cm(2) was observed at 90 K together with a relatively low electric coercive field of 0.32 MV/cm, although the ferroelectric hysteresis loops could not be observed at room temperature due to a high leakage current density. The temperature dependence of the ferroelectric hysteresis loops indicated that these hysteresis loops lose their shape above 165 K, and the nominal remanent polarization drastically increased due to the leakage current. Magnetic measurements indicated that the saturation magnetization was less than 1 emu/cm(3) at room temperature and increased to approximately 2 emu/cm(3) at 100 K, although the spontaneous magnetization could not appear. The magnetization curves of polycrystalline BiFeO3 film were nonlinear at both temperatures, which is different with BiFeO3 single crystal.     

Synthesis,structural and magnetic characterization of highly ordered single crystalline BiFeO3 nanotubes

In this work, we report on the fabrication of highly ordered single crystalline BiFeO₃ (BFO) nanotubes by a sol–gel technique using two-step anodic aluminum oxide (AAO) as template. We prepared BFO nanotubes with dimensions of 65 nm in diameter and 3 μm in length, as confirmed by scanning electron microscopy (SEM) measurements. The obtained single crystalline nanotubes present the expected pure phase (BiFeO₃) as confirmed by energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). In addition to the antiferromagnetic behavior, the magnetization curves of the BFO nanotubes also present a ferromagnetic response, which holds from 2 to 300 K. This desirable behavior is associated to the break of the antiferromagnetic helical spin ordering of the BFO nanotubes. Besides the magnetocrystalline anisotropy, the large length-to-diameter ratio induced an uniaxial shape anisotropy, attested by the applied magnetic field angle measurements.