Temperature Stable and Low Loss Microwave Dielectric Ceramics of Li₂Mg_3-xSr_xTiO₆

In this paper, a series of Li₂Mg_3-xSr_xTiO₆ (x = 0, 0.02, 0.04, 0.06, 0.08) ceramics were prepared by the conventional solid-state reaction method. The effects of Sr²⁺ substitution on the structure, morphology and microwave dielectric properties of Li₂Mg₃TiO₆ ceramics were investigated. The X-ray diffraction (XRD) results indicated that Li₂Mg₃TiO₆ and SrTiO₃ phases stably coexisted with each other and formed composite materilas. The appearance of porous structure mainly originated from the volatilization of lithium at high sintering temperatures. As the Sr²⁺ content increased from 0 to 0.08, the optimum dielectric constant (ε_r) increased from 13.61 to 17.32, the quality factor (Q×f) decreased monotonously and the temperature coefficient of resonant frequency (τ_f) changed from -34.4 to +16.8 ppm/°C. The variations of ε_r, Q×f and τ_f could be explained by the Lichtenecker logarithmic model and mixing rule, respectively. In particular, optimal microwave dielectric properties of ε_r = 16.08, Q×f = 82100 GHz, τ_f = +1.7 ppm/°C were obtained for Li₂Mg_2.94Sr_0.06TiO₆ ceramic sintered at 1310 °C for 5h.