Phase evolution and microwave dielectric properties of the Li2(1+x)ZnGe3O8 spinel oxides

Abstract

Recently, there have been considerable interests in the Li-containing spinel oxides as promising microwave dielectric materials. Li loss at elevated temperatures, however, is known to be inevitable, resulting in deterioration on dielectric performances. Here the influence of Li nonstoichiometry on the microwave dielectric properties of Li2ZnGe3O8, a spinel oxide, was reported. An appropriate level of Li excess enhanced the densification of Li2ZnGe3O8 and increased dielectric performances. In contrast, high level of Li excess induced the formation of the secondary phase of Li2ZnGeO4 confirmed by XRD and Raman spectra, which in turn lowered the dielectric properties. Typically, a composition with x = 0.075, in the Li2(1+x)ZnGe3O8 ceramics exhibited the enhanced microwave dielectric properties with er = 10.68, Q × f = 77,300 GHz (at 13.3 GHz), and τf = − 70.35 ppm/°C when sintered at 940 °C for 4 h. Moreover, these compounds have well chemical compatibility with the silver electrodes.