Preparation and characterisation of the magneto-electric xBiFeO(3)-(1-x)BaTiO3 ceramics

The solid solutions of BiFeO3-BaTiO3 have been prepared via solid state with a view to obtaining magnetoelectric properties, i.e. ferroelectric and magnetic activity in the same range of temperatures. Optimum calcination and sintering strategy for obtaining pure perovskite phase, dense ceramics (> 97% relative density) and homogeneous microstructures have been determined. The sample of composition 0.7BiFeO3-0.3BaTiO3 reported in the present work is pseudo-cubic at room temperature. The permittivity is epsilon(r) ~150 at the room temperature and shows a broad ferro-para phase transition at around 175 °C where epsilon(r) ~1600. This diffuse maximum of the permittivity, similar to that in relaxors, is due to the chemical inhomogeneity in both A and B sites of the perovskite unit cell ABO3. Higher losses, tan delta > 1, appear above 200 °C and other different conduction mechanisms start to be active particularly at temperatures higher than 400 °C, when the ceramic becomes conductive. The magnetic properties show a succession of transitions from weak ferro/ferrimagnetism-to-antiferromagnetism and anti ferromagnetism-to-paramagnetism at T-NI ~10 K and T-N2 ~265 K. Below T-N2 the ceramic 0.7BiFeO3-0.3BaTiO3 can present magnetoelectric coupling, due to the fact that is simultaneously ferroelectric and anti ferromagnetic.