Chemical bond features and microwave dielectric properties of olivine-type LiMSiO4 (M = Ho, In) ceramics

Orthorhombic olivine-structured LiMSiO 4 (M = Ho, In) ceramics were synthesised using the solid-state reaction. Promising microwave dielectric properties of ε r  = 10.04, τ f  = 23.3 ppm/°C and a high-quality factor ( Q  ×  f ) of 11,415 GHz for LiHoSiO 4 were obtained at 1050 °C, and ε r  = 7.78, τ f  = −46.8 ppm/°C and Q  ×  f  = 23,390 GHz for LiInSiO 4 were achieved at 1140 °C. According to the bond valence result, Ho 3+ presented a slightly compressed state but Li + and Si 4+ exhibited a strong rattling state in LiHoSiO 4 , which led to higher ε r than the ε theo . The integrated effect of rattling cations (Li + and In 3+ ) and a compressed cation (Si 4+ ) in LiInSiO 4 resulted in a small positive deviation Δ ε r . The larger packing fraction of LiInSiO 4 contributed to a higher Q  ×  f than LiHoSiO 4 . The Si–O bond in both ceramics played a leading role in influencing the Q × f according to the Phillips−Van Vechten−Levine chemical bond theory.