Effects of (Mg_1/3Nb_2/3)⁴⁺ substitution on the structure and microwave dielectric properties of 0.7CaTiO₃–0.3SmAlO₃ ceramics

0.7CaTi_1-x(Mg_1/3Nb_2/3)_xO₃–0.3SmAlO₃ (0 ≤ x ≤ 0.04) ceramics were prepared by solid-state reaction method. The effects of (Mg_1/3Nb_2/3)⁴⁺ substitution on crystal structure, microstructure, and microwave dielectric properties of the ceramics were investigated. The orthorhombic perovskite structure remains unchanged, but the dielectric properties are affected significantly by replacing Ti⁴⁺ with (Mg_1/3Nb_2/3)⁴⁺. The dielectric constant (ε_r) exhibits a slight decrease from 44.9 to 43.9, and the temperature coefficient of resonance frequency (τ_f) exhibits a transition from + 4.1 to ‒1.4 ppm/°C with the increase of x. An appropriate amount of (Mg_1/3Nb_2/3)⁴⁺ substitution can promote sintering and, thus, reduce dielectric loss. The ceramic with x = 0.02 sintered at 1390 °C shows excellent microwave dielectric properties: ε_r = 44.1, Q × f = 45 600 GHz, and τ_f =  + 0.8 ppm/°C.