Crystal structure, chemical bonds and microwave dielectric properties of ultra-low loss Li2Mg2GaTi2O8F ceramics

Ceramics of Li2Mg2GaTi2O8F (LMGTOF) were prepared by the traditional solid-state method. XRD and TEM results confirmed that a single phase of Li2Mg2GaTi2O8F, with an Fd-3m space group and a cubic spinel structure, was formed by the ceramics. It was shown by the results that the lattice parameters of the ceramics at 1050 °C were measured as a = b = c = 8.36576 Å, with a volume of V = 585.485549 Å3. Furthermore, it was observed through the analysis of the Raman peak at 718 cm−1 that an inverse relationship was exhibited between the Raman shift and εr. Similarly, an opposing trend was also demonstrated between the Q × f value and FWHM. By bond valence analysis, it was shown that Mg2+, Ga3+, and Ti4+ ions were in a "rattling" state, and the large positive deviation between εcorr and εtheo was attributed to the strong "rattling" effect induced by the cations. At 1050 °C, the best microwave dielectric properties (εr = 14.58, Q × f = 76,689 GHz, and τf = −52 ppm/°C) were exhibited by LMGTOF ceramics.