Spinel-type solid solution ceramic MgAl2O4-Mg2TiO4 with excellent microwave dielectric properties

In this work, a series of (1-x)MgAl2O4-xMg2TiO4 (expressed as (1-x)MA- xMT) (0.0 ≤ x ≤ 0.9) ceramics were successfully prepared via a solid-state reaction, and the effect of Mg2TiO4 content on the phase compositions, microstructures and microwave dielectric properties of MgAl2O4 ceramics have been investigated. The MgAl2O4 could form a solid solution with Mg2TiO4, and the grain size of the (1-x)MA-xMT ceramics gradually increased with the increase of sintering temperature. The dielectric constants (εr) of (1-x)MA-xMT ceramics steadily increased with the increase of Mg2TiO4 content. The εr values were mainly affected by secondary phase and dielectric polarizability. The quality factor (Qf) of (1-x)MA-xMT ceramics was closely related to the relative density, secondary phase, cation vacancies and Ti valence; whereas the temperature coefficient of resonance frequency (τf) highly depended on the Al-site bond strength. For the sample at x = 0.9, the 0.1MA-0.9MT ceramics sintered at 1350 °C for 4 h exhibited the optimized microwave dielectric properties: εr = 12.36, Qf = 236,600 GHz and τf = −61 ppm/°C.