Influence of Ca2+ substitution for Ba2+ on the crystal structure and microwave dielectric properties of Ba1−xCax(Mg1/3Ta2/3)O3 ceramics

Abstract

The Ba1–xCax(Mg1/3Ta2/3)O3 (BCMT, 0 ≤ x ≤ 0.05) microwave dielectric ceramics were synthesized by the conventional solid-state ceramic route. In this paper, the effects of Ca2+ substituting for Ba2+ on the phase structure, microstructure, and microwave dielectric properties of Ba1–xCax(Mg1/3Ta2/3)O3 ceramics were investigated. X-ray diffraction (XRD) exhibited that the Ba1–xCax(Mg1/3Ta2/3)O3 ceramics possessed the main phase Ba(Mg1/3Ta2/3)O3 (BMT) when 0 ≤ x ≤ 0.05 and secondary phase Ba0.5TaO3 for x = 0.05. SEM micrographs showed that the substitution of Ca2+ for Ba2+ could increase the grain size. The apparent density was influenced by the concentration of liquid phases caused by the substitution of Ca2+ for Ba2+ ions. The microwave dielectric properties depended heavily on apparent density, B-site cation ordering degree, Ba-deficient, secondary phase and distortion of oxygen octahedral. Finally, Ba1–xCax(Mg1/3Ta2/3)O3 (x = 0.04) ceramics sintered at 1450 °C for 8 h showed superior microwave dielectric properties of er = 24.1, Q × f = 165,800 GHz and τf = 0.12 ppm/℃.