Abstract:

Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application, especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission. Pure magnesium oxide (MgO), a kind of ceramic dielectric material, possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength, low dielectric constant, and low dielectric loss properties, but its application is limited by high sintering temperature during preparation. This work presented the preparation of a new type of multiphase ceramics based on MgO, which was MgO-1%ZrO₂-1%CaCO₃-x%MnCO₃ (MZCM_x, x = 0, 0.25, 0.50, 1.00, 1.50, in molar), and their phase structures, morphological features, and dielectric properties were investigated. It was found that inclusion of ZrO₂ and CaCO₃ effectively inhibited excessive growth of MgO grains by formation of second phase, while addition of MnCO₃ promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth, resulting in a lower ceramic sintering temperature. Excellent performance, including high dielectric strength (E_b = 92.3 kV/mm) and quality factor (Q × f = 216642 GHz), simultaneously accompanying low dielectric loss (< 0.03%), low temperature coefficient of dielectric constant (20.3×10^-6 ℃^-1, 85 ℃) and resonance frequency (-12.54×10^-6 ℃^-1), was achieved in MZCM_1.00 ceramics under a relatively low sintering temperature of 1350 ℃. This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.

Key words: MgO ceramic, dielectric strength, sintering temperature, growth activation energy