Cation distribution and bond energy of intermediate spinel Mg(Zn0.5Ti0.5)2xGa(2−2x)O4 microwave dielectric ceramics

Abstract

Substitution of Ga3+ by [Zn0.5Ti0.5]3+ in MgGa2O4 improved the comprehensive properties of the resultant spinel. A continuous solid solution with a spinel structure was formed in Mg(Zn0.5Ti0.5)2xGa(2−2x)O4 (0 ≤ x ≤ 1); here, Zn2+ occupied the tetrahedral 8a site while Ti4+ occupied the octahedral 16d site, resulting in a decrease in the degree of inversion λ from 0.86 to 0. The optimal sintering temperature decreased from 1460 °C to 1220 °C, and the dielectric constant (εr) increased from 8.8 to 14.9; these changes could be ascribed to the greater polarizability of [Zn0.5Ti0.5]3+ relative to that of Ga3+. The temperature coefficient of resonant frequency (τf) of the material remarkably increased from −64.1 ppm/°C to −16.8 ppm/°C, which may be attributed to the increase in dielectric polarizability/molecular volume, bond energy, and bond valence in B-sites. The high-quality factor (Q × f) slightly decreased from 89,253 GHz to 73,432 GHz with decreasing λ and packing fraction. Optimal microwave dielectric properties were obtained from the sample with x = 1 and sample sintered at 1220 °C; in this case, εr = 14.9, Q × f = 73,432 GHz, and τf = −16.8 ppm/°C.