Improving the microwave dielectric properties of Ga2[LiGa3]O8 inverse spinel by enhancing B-site ordering degree

A series of inverse spinel ceramics, Ga2 [Li1+xGa3]O8+δ (0.05 = x ≤ 0.125), were synthesized by the conventional solid-phase reaction. The addition of Li (x ≤ 0.1) increased the order degree of octahedra cations and caused an expansion in cell volume, and the maximum solution was located at 0.1–0.125. The dielectric constant of Ga2 [Li1+xGa3]O8+δ ceramics increased with the ionic polarizability of primitive unit cell, and the optimum microwave dielectric performances were obtained at x = 0.1 sample sintered at 1260 °C with er = 10.78 ± 0.1, Q × f = 171,171 ± 500 GHz, and τf = −56.47 ± 1.0 ppm/°C. The τf showed an opposite variation trend to that of the Ga1 bond valence and octahedron distortion. The Q × f was determined by the packing fraction and FWHM of 424 cm−1 Raman mode. In addition, the intrinsic dielectric properties of Ga2 [Li1+xGa3]O8+δ ceramics were evaluated by infrared reflectivity spectra. The results show that Ga2 [Li1+xGa3]O8+δ ceramic is a promising substrate material.