Chemical bond and microwave dielectric properties of two novel low-εr AGa4O7 (A = Ca, Sr) ceramics

Two novel low-εr microwave dielectric ceramics AGa4O7 (A = Ca, Sr; called CGO and SGO, respectively) were analyzed by XRD, SEM, and Raman spectroscopy, showed the monoclinic structure with a C2/c space group. Encouraging microwave dielectric properties (CGO: εr = 9.1, Q × f = 40 600 GHz (f = 12.4 GHz), and τf = −86.3 ppm °C−1; SGO: εr = 9.2, Q × f = 62 400 GHz (f = 14.6 GHz), and τf = −63.4 ppm °C−1) are obtained. The PVL chemical bond theory indicated that GaO bonds play a role in affecting the εr and Q × f values. The τf of AGa4O7 (A = Ca, Sr) had adjusted close to zero (0.93CGO-0.07CaTiO3:εr = 11.3, Q × f = 31,043 GHz, and τf = 3.97 ppm °C−1; 0.82SGO-0.18LiCa2Mg2V3O12：εr = 11.8, Q × f = 55,564 GHz, and τf = 5.62 ppm °C−1).