Effect of Li nonstoichiometry and TiO2 addition on the microwave dielectric properties of Li3PO4 ceramics

Li 3 PO 4 ceramic is a promising microwave ceramic material with low dielectric constant. The effect of Li nonstoichiometry on phase compositions, microstructures, and microwave dielectric characteristics of Li 3 PO 4 ceramics, on the other hand, has been examined infrequently. Therefore, in the first part of this study, the stoichiometry and Li nonstoichiometry compositions based on Li 3+x PO 4 (x = 0, 0.03, 0.06, 0.09, 0.12 and 0.15) were prepared by conventional solid-phase method. The results show that a few nonstoichiometric lithium ions enter the lattice of Li 3+x PO 4 . Compared with the chemical content of Li 3 PO 4 , the sintering characteristics, relative dielectric constants and quality factors of Li 3+x PO 4 ceramics can be improved by slightly excessive Li ions, while the properties of Li 3 PO 4 ceramics can be deteriorated by excessive Li ions. Li 3.12 PO 4 ceramics sintered at 975 °C for 2 h have good dielectric properties ( ε r  = 5.89, Q×f  = 44,000 GHz, τ f  = −206 ppm/ ° C). In order to improve its large negative temperature coefficient of resonant frequency, in the following study, rutile nano TiO 2 particles were added as τ f compensator. Adding TiO 2 powders not only effectively improve the temperature stabilities of the multiphase ceramics, but also make the grain growth more uniform. With the increase of TiO 2 content from 0.40 to 0.60, τ f increases from −73.5 ppm/ ° C to +42.3 ppm/ ° C. The best dielectric property of 0.45Li 3.12 PO 4 -0.55TiO 2 composite ceramic is ε r  = 13.29, Q×f  = 40,700 GHz, τ f  = +8.8 ppm/ ° C.