Synthesis of SmAlO₃ by polymeric precursor method and its microwave dielectric properties

SmAlO₃ microwave dielectric ceramic powder was successfully synthesized by the polymeric precursor method using EDTA as a chelating agent. The polymeric decomposition mechanism of the precursor, the formation process of SmAlO₃ and the properties of the particles were characterized. The results show that the dried gel including EG addition is decomposed completely up to 550°C and single SmAlO₃ phase with orthorhombic perovskite structure is found when the calcining temperature is increased to 800°C. Compared with the conventional solid-state reaction route, the synthesis temperature is sharply decreased from 1400 to 800°C. With the average particle size of about 30 nm, the particles of the as-synthesized powder are uniform and spherical. Using the as-synthesized powder as raw material, the sample sintered at 1550°C for 2 h possesses the highest relative density of 97.5% and exhibits excellent microwave dielectric properties of relative permittivity ε_r=21, quality factor Q_f=77400 GHz and temperature coefficient of resonant frequency τ_f=-73.2×10^-6°C^-1.