Effect of chemical bond characteristics on the microwave dielectric properties of olivine-type LiTmRO4 (R = Si, Ge) ceramics

Orthorhombic olivine-structured LiTmRO 4 (R = Si, Ge) ceramics were synthesized using a solid-state reaction. Promising microwave dielectric properties of ε r  = 8.18, τ f  = 13.7 ppm/°C and a high-quality factor ( Q  ×  f ) of 24,274 GHz for LiTmSiO 4 were obtained at 1130 °C, and ε r  = 8.67, τ f  =  − 24.4 ppm/°C and Q  ×  f  = 19,231 GHz for LiTmGeO 4 were achieved at 1090 °C. According to the bond valence results, Tm 3+ and Ge 4+ presented a compressed state, but Li + exhibited a strong rattling state in LiTmGeO 4 , which led to a higher ε r than ε theo . The integrated effect of the rattling cations (Li + and Si 4+ ) and a compressed cation (Tm 3+ ) in LiTmSiO 4 resulted in a smaller positive deviation ∆ ε r . The larger packing fraction of LiTmSiO 4 contributed to a higher Q  ×  f than that of LiTmGeO 4 . 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.