Structure characteristics and enhanced microwave dielectric properties of Ba(Mg1/3Nb2/3)O3–Mg2SiO4 composite ceramics with a tunable τf

Abstract

The performance of microwave communication devices widely used in 5G network is strongly determined by the properties of dielectric ceramics used in the fabrication, which are required to have a suitable dielectric constant (εr), high Q × f value and near-zero temperature coefficient of resonant frequency (τf). In this work, (1-x)Ba(Mg1/3Nb2/3)O3–xMg2SiO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5) composite ceramics meeting the application requirements have been developed and investigated. Ba(Mg1/3Nb2/3)O3 and Mg2SiO4 could coexist without any unexpected phases due to the different crystal structures and coordination relationship. The sintering behavior and the structural changes of Ba(Mg1/3Nb2/3)O3 were specifically relevant to the microwave dielectric properties. Introducing appropriate Mg2SiO4 content promoted the sintering of Ba(Mg1/3Nb2/3)O3 and the maximum Q × f value of 110,000 GHz was obtained at the sample with x = 0.3 sintered at the optimized temperature of 1420 °C. Due to the low dielectric loss and the opposite sign τf value of Mg2SiO4, the composite ceramic successfully adjusted the τf value to near zero while maintaining a high Q × f value. However, the experimentally measured values of εr and τf were significantly different from the theoretically calculated values due to the “rattling” effect of B-site cations and the enhanced symmetry of oxygen octahedra in Ba(Mg1/3Nb2/3)O3. These structural changes were confirmed by the results of bond valence analysis and Raman vibration spectra. The 0.6Ba(Mg1/3Nb2/3)O3–0.4Mg2SiO4 ceramic sintered at 1420 °C exhibits competitive microwave dielectric properties: εr = 18.9, Q × f = 91,000 GHz (at 8.016 GHz) and τf = 2.6 ppm/°C, which indicates it a promising application prospect of microwave communication.