Crystal Chemistry, Raman Spectra, and Bond Characteristics of Trirutile-Type CoTiTaO Microwave Dielectric Ceramics.

A novel trirutile-type CoTiTaO ceramic was reported here for the first time. The correlations between the sintering behavior, crystal structure, chemical bond, and dielectric properties were investigated. Pure CoTiTaO ceramic was synthesized in the temperature range of 1000-1100 °C. A trirutile structure and refined parameters of a = b = 4.71163 Å, c = 9.13586 Å, and V = 202.811 Å could be obtained (1075 °C). According to the P-V-L chemical bond theory, majority contributions to the dielectric constant originated from Ta-O bonds, owing to its largest bond ionicity and bond susceptibility values. The experimental dielectric constant is close to the theoretical values calculated via the P-V-L chemical bond theory and Clausius-Mossotti relationship. The Ta-O bonds that present the largest lattice energy are also the main factors influencing the intrinsic loss. The τ value is consistent with the oxygen distortions of the octahedron. More importantly, variations of the densification, average grain size, and grain boundary are crucial factors for development of the microwave dielectric properties. The Raman spectra and group theory were analyzed together, and the results indicated that the A mode at 687.45 cm, which reflects the stretching vibrations of the O anions, dominates the Raman vibrations. Typical microwave dielectric properties of CoTiTaO ceramics were obtained when sintered at 1075 °C: ε = 40.69, Qf = 17291 GHz, and τ = 114.54 ppm/°C.