Correlations between microwave dielectric properties and crystal structures of Sb-doped Co_0.5Ti_0.5NbO₄ ceramics

Co_0.5Ti_0.5Nb_1-xSb_xO₄ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics with low dielectric losses were fabricated by the conventional solid-state reaction method. A single-phase tetragonal rutile structure with a superlattice diffraction peak was observed. The temperature coefficient of resonant frequency (τ_f) decreased with an increase in oxygen octahedron distortion. The quality factor (Q × f) was increased owing to the enhanced cation ordering, which reduced the lattice energy and internal stress of the oxygen octahedron. Sb³⁺ was transformed into Sb⁵⁺, while the transformation of Co²⁺ to Co³⁺ was inhibited. The as-prepared Co_0.5Ti_0.5Nb_0.5Sb_0.5O₄ ceramic exhibited ε_r of 38, Q × f of 32,047 GHz, and τ_f of 32.6 parts-per-million/°C.