Dielectric and multiferroic properties of 0.75BiFeO_3-0.25BaTiO_3 solid solution

摘要

Solid solution 0.75BiFeO_3-0.25BaTiO_3 (BFO-25 % BT) was prepared by solid state reaction method. Powder X-ray diffraction showed the morphotropic phase boundary (MPB) with the coexistence of both rhombohe-dral and cubic phases due to splitting in the line at 2θ = 39.7°. Scanning electron micrographs indicated that the ceramic has compact and uniform microstructure with average grain size ＜3 μm. The polarization vs applied electric field analysis showed an unsaturated hysteresis loop with the remnant polarization 12.95 μC/cm~2 at 22 kV/cm for 0.75BiFeO_3-0.25BaTiO_3 ceramic. The calculations of diffuse parameter i.e. slope γ = 1.63 suggested a high degree of diffusion in BFO-BT lattice. The room temperature magnetic measurements confirmed the weak ferromagnetism of magnetization ～0.1 emu/gm at an applied magnetic field of H = 5 kOe for 0.75BiFeO_3-0.25BaTiO_3 ceramic. The high temperature magnetic and dielectric analysis suggested a coupling between ferroelectric and magnetic parameters near the antiferromagnetic-paramagnetic transition T_c ～ 310 ℃, which was responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy and complex modulus analysis confirmed the conventional relaxor, NTCR (negative temperature coefficient of resistance), giant ferroelectricity and polydispersive non-Debye type dielectric relaxation behaviour for 0.75BiFeO_3-0.25BaTiO_3 ceramic at 170 ℃ on 1 kHz with activation energy 2.33 eV. The modulus analysis also confirmed the possibility of hopping mechanism for electrical transport process in material.