Crystal structure and microwave dielectric properties of two novel garnet-type ceramics with Ga3+/V5+ cations on tetrahedral site

In this study, a strategy involving the incorporation of non-adjacent valence state cations into tetrahedral sites was employed. Microwave dielectric ceramics with the composition Ca 3 M 2 Ga 2.5 V 0.5 O 12 (M=Sn and Zr) were designed and synthesized using a solid-state reaction method. The crystal structure of these ceramics has been verified as cubic garnet with the Ia -3 d space group. Ca 3 Sn 2 Ga 2.5 V 0.5 O 12 and Ca 3 Zr 2 Ga 2.5 V 0.5 O 12 ceramics sintered at optimal temperatures exhibited favorable microwave dielectric properties, with Q  ×  f values of 18, 571 GHz and 13,370 GHz, ε r of 9.65 and 9.34, and τ f values of − 43.1 ppm/°C and − 36.4 ppm/°C, respectively. The difference in ε r is primarily attributed to the ionic polarizability per unit volume and bond ionicity. The higher Q  ×  f value of the Ca 3 Sn 2 Ga 2.5 V 0.5 O 12 ceramic correlates with its larger packing fraction, narrower Raman full width at half maximum, stronger average bond covalency, and higher total lattice energy. In contrast, the smaller | τ f | of Ca 3 Zr 2 Ga 2.5 V 0.5 O 12 is associated with its larger bond valence at the B-site, lower oxygen bond valence, and higher bond energy. Analysis using the Phillips−Van Vechten−Levine (P−V−L) theory and bond valence calculations demonstrates that the M 4+ cations occupying the octahedral sites have a significant impact on the microwave dielectric properties. Furthermore, a dielectric resonator antenna based on Ca 3 Sn 2 Ga 2.5 V 0.5 O 12 was designed for C-band communication (4−8 GHz).