An evaluation of the impact of crystal structure on microwave dielectric properties of novel titanite-type CaMGeO5 ceramics

Abstract

Novel titanite-type CaMGeO5 (M = Ge, Hf, Zr) microwave dielectric ceramics were prepared using solid-state reaction. A CaGe2O5 single-phase ceramic with a triclinic structure was obtained, and the main phase compositions and crystal structure of CaMGeO5 (M = Hf, Zr) ceramics were confirmed. The CaGe2O5 single-phase ceramic exhibited a high Q×f value (92,400 GHz), and its Q×f values were controlled by the rc (Ge-O) and the packing fraction. For CaMGeO5 (M = Hf, Zr) multi-phase ceramics, the Q×f values were deteriorated by the second phase. The τf and τε values of the CaMGeO5 ceramics were directly controlled by the εr anomaly peaks, and the phase transitions were controlled by −δ. The τf values of the CaMGeO5 (M = Ge, Hf, Zr) ceramics were mainly related to −δ, and the small −δ corresponded to the nearer-zero τf values for the titanite-type CaMGeO5 ceramic with negative τf values. The optimal microwave dielectric properties (εr = 10.57, Q×f = 92,400 GHz at 13.22 GHz, and τf = 68.3 ppm/°C) were obtained by the CaGe2O5 ceramic.