Preparation and Functional Properties of BaTiO-BaGeO Ceramics.

The phase formation and functional properties (dielectric, ferroelectric switching, and tunability) in x BaGeO-( 1- x )BaTiO 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 BaTiO 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 α -BaGeO phase and tetragonal BaTiO, and shows permittivity below 100 and a lossy linear dielectric character, with zero tunability and lack of switching, similar as the BaGeO 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 optimum in the present ceramic series: it shows the highest relative density of 99% and large grains (tens of micrometers), excellent switching properties with the highest polarization and a rectangular switching loop, the highest permittivity above room temperature and a good ε(E) tunability of 60%-70%, comparable with the best values reported in other BaTiO solid solutions.