Preparation and Functional Properties of BaTiO3–BaGeO3 Ceramics

Abstract

The phase formation and functional properties (dielectric, ferroelectric switching, and tunability) in <inline-formula> <tex-math notation= LaTeX >${x}$ </tex-math></inline-formula>BaGeO₃–(<inline-formula> <tex-math notation= LaTeX >$1- {x}$ </tex-math></inline-formula>)BaTiO₃ ceramics with compositions <inline-formula> <tex-math notation= LaTeX >${x} =0$ </tex-math></inline-formula>, 0.01, 0.018, 0.1, 0.68, and 1, produced by solid-state reaction, are presented. For small Ge additions <inline-formula> <tex-math notation= LaTeX >${x} \\le {0.10}$ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation= LaTeX >${x} = {0.68}$ </tex-math></inline-formula> is a composite containing mostly nominal amounts of hexagonal <inline-formula> <tex-math notation= LaTeX >$\\alpha $ </tex-math></inline-formula>-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 (<inline-formula> <tex-math notation= LaTeX >${x} = {1}$ </tex-math></inline-formula>). The role of Ge in increasing the density by liquid-phase sintering is beneficial for improving the electrical properties. In this sense, the composition <inline-formula> <tex-math notation= LaTeX >${x} = {0.10}$ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation= LaTeX >$\\varepsilon ({E})$ </tex-math></inline-formula> tunability of 60%–70%, comparable with the best values reported in other BaTiO₃ solid solutions.