Combined effect of rattling and compression on the microwave dielectric properties of B-site 1:3 ordered Li6A7Ti11O32 (A = Zn, Mg) spinels

Abstract

Dense ceramics of two B-site 1:3 ordering spinels Li6A7Ti11O32 (A = Zn, Mg) with space group P4332 were prepared by solid-state reaction. Raman spectroscopy and XRD analysis revealed why the lattice parameters and volume of Li6Mg7Ti11O32 are abnormally greater than those of Li6Zn7Ti11O32. Li6Zn7Ti11O32 exhibits outstanding microwave dielectric properties (Q × f = 129,600 GHz (8.9 GHz), εr = 20.7, τf = −45 ppm/°C) and a low thermal expansion coefficient (αL) of 5.5 ppm/°C. While Mg-analogue displayed a lower Q × f ∼108,600 GHz (9.1 GHz), a lower αL ∼ 4.9 ppm/°C, a higher εr ∼ 21.9, and a slightly positive offset τf ∼ −21 ppm/°C relative to Li6Zn7Ti11O32. A significant positive deviation of 91.6% was observed between the corrected εr(corr) by the porosity and the calculated εr(C-M) by the Clausius-Mosotti (C-M) equation in the Li1.33xA2-2xTi1+0.67xO4 solid solution. The variation in εr and τf values of Li6A7Ti11O32 (x = 0.5625) compared to Li2ATi3O8 (x = 0.75) might be attributed to the combined effect of rattling and compression cations at A-site and B-site. Moreover, the negative τf of Li6A7Ti11O32 (A = Zn, Mg) ceramics was balanced to near zero by adding CaTiO3.