Effect of La2O3 addition on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

Abstract

In this paper, Ba(Mg1/3Ta2/3)O3 (BMT) ceramics with x (x = 0–5) wt% La2O3 were prepared by the conventional solid-state ceramic route for investigating the effect of La2O3 addition on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics. The XRD results showed that the main crystal phase in the sintered ceramics was Ba(Mg1/3Ta2/3)O3 and the secondary phase Ba0.5TaO3 was presented depending on the La2O3 contents. SEM photographs suggested that La2O3 working as sintering additives promoted the densification and grain growth. Proper La3+ substituted for Ba2+ site in Ba(Mg1/3Ta2/3)O3, which led to the reduction of lattice parameters of Ba(Mg1/3Ta2/3)O3. And the result had positive effect on the dielectric properties, especially the Q × f value. As increasing La2O3 content from 0 to 5 wt%, the dielectric constant (er) increased from 24.9 to 26.3, and the Q × f value increased first from 58,000 GHz to the peak value of 112,000 GHz (4 wt% La2O3) and thereafter decreased to 68,000 GHz. Meanwhile the temperature coefficient of resonant frequency (τf) decreased first to a minimum value and increased thereafter. At last, Ba(Mg1/3Ta2/3)O3 ceramics with 4 wt% La2O3 sintered at 1400 °C for 5 h had compact and homogeneous microstructure and possessed excellent microwave dielectric properties: high dielectric constant er = 25.9, high Q × f = 112,000 GHz, and near-zero τf = +0.3 ppm/°C.