Preparation and microwave dielectric properties of Li(Mg_(1-x)Co_x)PO_4 ceramics for low-temperature cofired ceramic applications

摘要

Li(Mg_(1-x)Co_x)PO_4 (x=0-0.09) ceramics were prepared by the conventional solid-state ceramic method. The formation of single-phase Li(Mg_(1-x)Co_x)PO_4 solid solutions is confirmed by the X-ray diffraction (XRD) patterns. Co~(2+) substitution for Mg~(2+) can lower the sintering temperature and enhance the Qf value of LiMgPO_4 ceramics. The Li(Mg_(0.95)Co_(0.05))PO_4 ceramic sintered at 875℃ reaches a maximum relative density of 97.4% and shows the microwave dielectric properties of ε_r=6.97, Qf-111,200 GHz, and τ_f=-53.8 ppm/℃. The negative τ_f value can be tuned nearly to zero by adding TiO_2. The Li(Mg_(0.95)Co_(0.05))PO_4-TiO_2 composite ceramic with 16.1 wt% TiO_2 sintered at 875℃ for 2 h shows a near-zero τ_f value of +0.8 ppm/℃, together with an ε_r 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.