Preparation and functional properties of BaTiO3-BaGeO3 ceramics.

The phase formation and functional properties (dielectric, ferroelectric switching and tunability) in xBaGeO3-(1-x)BaTiO3 ceramics with compositions x = 0, 0.01, 0.018, 0.1, 0.68 and 1, produced by solid state reaction, are presented. For small Ge additions x0.10 for which the perovskite tetragonal phase is predominant, the low field dielectric properties are quite similar to ones of BaTiO3 ceramics, with all the structural phase transitions in the same temperature range and a small shift of the Curie temperature to higher values when increasing Ge addition. The eutectic composition x=0.68 is a composite containing mostly nominal amounts of hexagonal -BaGeO3 phase and tetragonal BaTiO3 and shows permittivity below 100 and a lossy linear dielectric character, with zero tunability and lack of switching, similar as the BaGeO3 composition (x=1). The role of Ge in increasing the density by liquid phase sintering is beneficial for improving the electrical properties. In this sense, the composition x=0.10 is an optimum in the present ceramic series: it shows the highest relative density of 99% and large grains (tens of m), excellent switching properties with the highest polarization and a rectangular switching loop, the highest permittivity above room temperature and a good (E) tunability of 60-70%, comparable with the best values reported in other BaTiO3 solid solutions.