Effect of chemical bond characteristics on the microwave dielectric properties of olivine-type LiTmRO4 (R = Si, Ge) ceramics
摘要
Orthorhombic olivine-structured LiTmRO4 (R = Si, Ge) ceramics were synthesized using a solid-state reaction. Promising microwave dielectric properties of εr = 8.18, τf = 13.7 ppm/°C and a high-quality factor (Q × f) of 24,274 GHz for LiTmSiO4 were obtained at 1130 °C, and εr = 8.67, τf = − 24.4 ppm/°C and Q × f = 19,231 GHz for LiTmGeO4 were achieved at 1090 °C. According to the bond valence results, Tm3+ and Ge4+ presented a compressed state, but Li+ exhibited a strong rattling state in LiTmGeO4, which led to a higher εr than εtheo. The integrated effect of the rattling cations (Li+ and Si4+) and a compressed cation (Tm3+) in LiTmSiO4 resulted in a smaller positive deviation ∆εr. The larger packing fraction of LiTmSiO4 contributed to a higher Q × f than that of LiTmGeO4. The R–O bond in both ceramics played a leading role in influencing Q × f according to the Phillips–Van Vechten–Levine chemical bond theory.