Structural and electrical properties of Gd-doped BiFeO_3:BaTiO_3 (3:2) multiferroic ceramic materials

摘要

Gadolinium doped BiFeO3:BaTiO3 (3:2) polycrystalline multiferroic ceramics have been prepared by high-temperature solid state reaction technique. X-ray diffraction (XRD) analysis at room temperature of the prepared materials confirmed the formation of the compounds with rhombohedral crystal structure. The average particle size of as prepared samples have been found in the range of 35nm to 55nm for different doping concentrations. The average grain size of as prepared samples are less than 100nm which is confirmed from SEM study. The SEM of annealed compounds showed the uniform distribution of grains and the formation of dense ceramic with average grain size in the order of 4 mu m. Dielectric studies of the materials reveals that the dielectric constant (epsilon r) and tangent loss (tan) decreases with doping concentrations at room temperature. The variation of epsilon r and tan with temperature was explained on the basis of Maxwell-Wagner mechanism. The values of grain resistance (Rb) and grain capacitance (C-b) were obtained from Nyquist plots for the different doping concentrations at 300 degrees C. The activation energy (Ea) was calculated from the curve of frequency dependent ac conductivity (sigma ac) within the range 0.19eV to 0.45eV. The remnant polarization of the samples (0.53 mu C/cm(2)) was measured from polarization versus electric field (P-E) hysteresis curves. The ferromagnetic behaviour of the Gd-doped BiFeO3:BaTiO3 (3:2) sample has been studied by SQUID for the lowest doping concentration. The value of remnant magnetization was found 0.0235 emu/g at room temperature.