Dielectric properties of the (1-x)BiFeO3-xBaTiO3 multiferroic ceramics

The solid solutions of (1-x)BiFeO3 - xBaTiO3 with x=0.20 and x=0.30 have been prepared via solid state, by sintering in air or in oxygen atmosphere. Optimum calcination and sintering strategy for obtaining pure perovskite phase, dense ceramics (>97% relative density) and homogeneous microstructures have been determined. Rhombohedral structure for x=0.20 and a pseudo-cubic one (low distortion) for the x=0.30 ceramics were obtained. In spite of the excellent microstructures and phase purity, the ferroelectric-paraelectric transitions at ~145°C and ~230°C for x=0.30 and x=0.20, respectively, found by differential calorimetry study were not confirmed by the dielectric spectroscopy investigations. The dielectric response shows multiple relaxations, high losses mainly at low frequency and high temperatures, which are signs of space charge or Maxwell Wagner phenomena. The complex impedance response for the ceramics sintered in oxygen shows in addition grain boundary effects. It results that in such ceramics, the dielectric response is strongly affected by the extrinsic phenomena rather than by the intrinsic ferroelectric response. The extrinsic properties are impossible to be fully controlled by normal ceramic processing. However, at room temperature and frequencies above 500 kHz, even these ceramics accomplish the dielectric properties requirements for further magnetoelectric applications.