Mechanism of ionic polarizability, bond valence, and crystal structure on the microwave dielectric properties of disordered Li10MTi13O32 (M = Zn, Mg) spinels

Abstract

The influence mechanism of the microwave dielectric properties of disordered spinels (Fd3̄m) Li10MTi13O32 (M = Zn, Mg) was investigated via Rietveld structural refinement, ionic polarizability, bond valence, P-V-L theory, Raman spectroscopy, and DC conductivity. For Li10ZnTi13O32 and Li10MgTi13O32, promising microwave dielectric properties of ϵr = 28.23 ± 0.3 and 29.23 ± 0.3, Q × f = 35 800 ± 500 GHz and 32 100 ± 500 GHz (at ∼7.5 GHz), and τf = −17.06 ± 2.0 ppm per °C and −11.05 ± 2.0 ppm per °C, respectively, were obtained at 980 °C. Bond valences reveal that almost all cations are rattling, weakening the bond strengths and widening the molecular dielectric polarizability. The expansion structures also result in τf values closer to zero and lower Q × f values. The bond ionicity and lattice energy of the Ti-O bonds are much greater than those of other bonds, indicating that the Ti-O bond is a major contributor to ϵr and Q × f. Moreover, the DC conductivity clarified that the Q × f values of the disordered spinels Li10ZnTi13O32 and Li10MgTi13O32 are not as high as other ordered spinels because of the transport of Li+ ions in their structures.