Microstructures and Microwave Dielectric Properties of the CaSmAlO4-Based Ceramics.

The effects of secondary phases on microwave dielectric properties were investigated for CaSmAlO4-based ceramics with bulk compositions of (2+2 x)CaO·(1− x)Sm2O3·Al2O3 ( x=−0.10, −0.05, 0, 0.05, 0.10) and (2+2 x)CaO·Sm2O3·Al2O3 ( x=0.02, 0.04). In dense ceramics with bulk compositions of (2+2 x)CaO·(1− x)Sm2O3·Al2O3, Ca3Al2O6 ( x>0) and SmAlO3 ( x≤0) secondary phases were observed. Moreover, Sm2O3 was detected for x<0, while CaO was only detected at x=0.2. The secondary phases of Ca3Al2O6 and SmAlO3 increased the dielectric loss (tan δ) and the temperature coefficient of the resonant frequency (τf). In dense ceramics with bulk compositions of (2+2 x)CaO·Sm2O3·Al2O3 ( x=0.02, 0.04), the additional CaO eliminated the SmAlO3 secondary phase and led to the formation of a CaSmAl3O7 secondary phase. Microwave dielectric properties were greatly improved for ceramics with bulk compositions of (2+2 x)CaO·Sm2O3·Al2O3 ( x=0.02, 0.04): ℇr=19.2; Q× f=120 000–120 400 GHz; τf=−10 to −9 ppm/°C. [ABSTRACT FROM AUTHOR]