Microwave dielectric properties of novel glass-free low temperature firing ACa 2 Mg 2 V 3 O 12 (A=Li, K) ceramics

Abstract Two novel low-firing microwave dielectric ceramics ACa2Mg2V3O12 (A=Li, K) were prepared using the solid state reaction method. The phase composition, sintering behavior, and microwave dielectric properties were investigated. X-ray diffraction (XRD) analysis showed that both ceramics crystallized into a cubic garnet structure. Both ceramics were well densified at temperatures lower than 960 °C. LiCa2Mg2V3O12 ceramic sintered at 940 °C with relative density of ~96.3% obtained the optimum microwave dielectric properties with er ~9.8, Q×f ~24,900 GHz (at 11.0 GHz), τf ~+259.2 ppm/°C. For KCa2Mg2V3O12, the ceramic sintered at 900 °C had a relative density of ~96.1%, a relative permittivity (er) ~10, a quality factor (Q×f) ~30,330 GHz and a large positive temperature coefficient of resonance frequency τf ~+190.9 ppm/°C. Both ACa2Mg2V3O12 (A=Li, K) ceramics were chemically compatible with Ag electrodes. The large positive τf of LiCa2Mg2V3O12 ceramic could be compensated by forming sold solution with NaCa2Mg2V3O12, and improved properties with a near-zero τf=+2 ppm/°C, er=9.9, Q×f=45,500 GHz was obtained for 0.16LiCa2Mg2V3O12–0.84NaCa2Mg2V3O12 ceramic sintered at 920 °C for 4 h.