Microwave Dielectric Behavior of CoTiTa2O8-MgNb2O6 Composite Ceramics: A Focus on Temperature Stability and Compositional Effects

Microwave dielectric (1 − x)CoTiTa2O8-xMgNb2O6 composite ceramics (x = 0.625–0.725) were fabricated through a two-step method and sintering techniques. The applied CoTiTa2O8 and MgNb2O6 powders were both synthesized by calcining stoichiometric mixtures of their respective metal oxides at 1000 °C for 3 h. The optimal sintering parameters were determined using visual high-temperature deformation analysis. The influence of the MgNb2O6 content on the phase composition, microstructure, and microwave dielectric properties of the obtained composite ceramics was comprehensively investigated. It was observed that an increase in the MgNb2O6 content resulted in a reduction in the dielectric constant (εr) and a significant enhancement in the quality factor (Q × f). The ceramics with a compositional value of x = 0.675, sintered at 1193 °C for 4.5 h, demonstrated a near-zero temperature coefficient of the resonant frequency (τf), exhibiting optimal microwave dielectric properties: εr = 28.4, Q × f = 33,055 GHz, and τf = −3.1 ppm/°C. These findings underscore the potential of the present CoTiTa2O8-MgNb2O6 composite ceramics for advanced microwave applications.