Electrical properties of Fe-doped BaTiO3

The polymorphism of BaTi1-xFexO3-delta solid solutions: 0 < x < 0.1, prepared by a sol-gel method, has been determined and presented in the form of a temperature-composition phase diagram for T > similar to 1000 degrees C. With increasing x, the high temperature hexagonal polymorph is stabilised to increasingly lower temperatures. The temperature of the tetragonal to cubic transition also decreases with increasing x, as shown by a combination of permittivity measurements, DSC and X- ray powder diffraction. The electrical properties of ceramics of tetragonal/cubic solid solutions, determined by impedance spectroscopy, show a ferroelectric bulk phase (for T < T-c) and a Schottky barrier associated with the grain boundaries whose resistance is sensitive to a dc bias voltage. The bulk properties are sensitive to sample heat treatment and in particular, for samples reheated in air <= 700 degrees C, oxidation occurs, generating Fe4+ and an increase in the level of p-type conductivity.