Crystal structure and microwave dielectric properties of Li2Mg0.6−xCoxZn0.4SiO4 ceramic for LTCC applications

In this work, Li2Mg0.6−xCoxZn0.4SiO4 ceramics (x = 0–0.4) added with 3 wt% Li2O–B2O3–Bi2O3–SiO2 (LBBS) glass were synthesised using the solid-state reaction method. The effects of substituting Co2+ for Mg2+in Li2Mg0.6−xCoxZn0.4SiO4 ceramics on crystal structure, microstructure, densification, crystallisation and microwave dielectric properties were investigated. X-ray diffraction patterns showed that monoclinic Li2MgSiO4, monoclinic Li2ZnSiO4 and orthorhombic Li2CoSiO4 formed finite solid solution in Li2Mg0.6−xCoxZn0.4SiO4 ceramics. Clear grain boundaries were observed via scanning electron microscopy. The substitution of Co2+ for Mg2+ increased grain size, densification, crystallinity degree and dielectric constant; it also reduced the dielectric loss of the ceramics to a certain extent. The absolute values of τf were positively related to the crystallinity degree. Li2Mg0.55Co0.05Zn0.4SiO4 ceramic added with 3 wt% LBBS and sintered at 900 °C exhibited considerable microwave dielectric properties of εr = 5.8, Q × f = 47,518 GHz and τf = −74.8 ppm/°C. Therefore, the ceramic is considered a candidate low-temperature co-fired ceramic material for substrate and filter applications.