Preparation and microwave dielectric properties of Li(Mg1-xCox)PO4 ceramics for low-temperature cofired ceramic applications

Li(Mg1-xCox)PO4 (x=0-0.09) ceramics were prepared by the conventional solid-state ceramic method. The formation of single-phase Li(Mg1-xCox)PO4 solid solutions is confirmed by the X-ray diffraction (XRD) patterns. Co2+ substitution for Mg2+ can lower the sintering temperature and enhance the Qf value of LiMgPO4 ceramics. The LiMg0.95Co0.05PO4 ceramic sintered at 875 °C reaches a maximum relative density of 97.4% and shows the microwave dielectric properties of εr=6.97, Qf=111,200 GHz, and τf=-53.8 ppm/°C. The negative τf value can be tuned nearly to zero by adding TiO2. The LiMg0.95Co0.05PO4-TiO2 composite ceramic with 16.1 wt% TiO2 sintered at 875 °C for 2 h shows a near-zero τf value of +0.8 ppm/°C, together with an εr value of 9.97 and a Qf value of 58,200 GHz. The composite ceramic does not react with the commonly used electrode material silver and is a promising candidate for low-temperature cofired ceramic applications.