Germanium substituted Li2Sn1-xGexO3 ceramics with improved sintering behavior, microwave dielectric properties and temperature stability

Abstract In this contribution, the Li2Sn1-xGexO3 (0 ≤ x ≤ 0.09) ceramics were synthesized by the conventional solid-state reaction method. The XRD patterns revealed that the solid solution was formed in the range of 0 ≤ x ≤ 0.07, and the Li2GeO3 secondary phase was detected in the x = 0.09 sample. The Rietveld refinement results showed a decrease in the cell volume. The crystal structural changes were further verified by TEM and STEM-EDS technologies. Because of the lower atomic weight and smaller ion radius of Ge4+ to that of the Sn4+ ions, the increased ionic diffusion rate improved the average grain sizes and decreased the porosity, but led to abnormal grain growth for x ≥ 0.05. The relative density first increased and then decreased; the relative permittivity (er) decreased with the increase of x due to the pronouncedly decreasing ionic polarizability; the Q × f values increased first with the increasing x and deteriorated because of the abnormal grain growth in the x ≥ 0.05 samples; the temperature coefficient of the resonant frequency (τf) decreased continuously owing to the “polarizability” effect. Typically, the optimum properties were achieved in the x = 0.07 sample that was sintered at 1175 °C for 4 h with ϵr = 14.53, Q × f = 58,300 GHz (f = 9.9 GHz), and τf = 2.4 ppm/°C, which is promising for industrial applications.