Sintering behavior, structures, and microwave dielectric properties of (Li_xNb_3x)Ti_1-4xO₂

(Li_xNb_3x)Ti_1-4xO₂ (0.05≤x≤0.23) ceramics were synthesized by conventional solid-state reaction method. The sintering behavior, structures, and microwave dielectric properties were investigated as a function of the content of (Li _1/4Nb_3/4)⁴⁺ substitution for Ti⁴⁺. Tetragonal rutile solid solutions were observed when 0.05≤x≤0.15, while LiNb₃O₈ phase coexisted with rutile phase when 0.20≤x≤0.23. Without sintering aids, (Li_xNb_3x) Ti_1-4xO₂ ceramics were well densified at 960°-1020°C. Dielectric constant (ε_r) changed from 91 to 39 and temperature coefficient of the resonant frequency (TCF) shifted from +320.5 ppm/°C to -72.7 ppm/°C with the amount of (Li _1/4Nb_3/4)⁴⁺ substitution increasing. (Li _0.215Nb_0.645)Ti_0.14O₂ ceramic sintered at 1020°C showed excellent microwave dielectric properties with ε_r∼43, Q × f value∼14 500 GHz and TCF∼-15 ppm/°C. The relationship between structure parameter (tetragonality ratio) and dielectric constant or/and TCF value of Li_xNb_3xTi _1-4xO₂ rutile solid solutions was also studied in this work.