Crystal structure, sintering behavior, and microwave dielectric properties of LiF-tailored high entropy Li2Mg6ZnTi6O20 ceramics

Abstract

This study designs and synthesizes highly dense Li₂Mg₆ZnTi₆O₂₀ microwave dielectric ceramics based on a high-entropy strategy, focusing on achieving stable structures, low sintering temperatures, and excellent comprehensive performance. The ceramics exhibit a predominant face-centered cubic disordered phase (Fd-3m) sintered at 1200–1280°C, alongside an increased presence of the second phase MgTiO₃ at higher temperatures. Remarkably, these ceramics demonstrate excellent microwave dielectric properties (ε_r = 16.69, Q × f = 88,230 GHz, and τ_f = −36.5 ppm/°C). Additionally, we have explored the addition of x wt% LiF (1 ≤ x ≤ 5) to the Li₂Mg₆ZnTi₆O₂₀ ceramics to enhance their applicability. The ceramics feature a spinel structure for LiF contents up to 3 wt%, while higher LiF concentrations induce the formation of a secondary phase, LiTiO₂, characterized by a rock salt structure. Notably, the lattice distortion induced by LiF leads to a constant decrease in ε_r. A moderate degree of lattice distortion serves to enhance the lattice stability of ceramics, which is reflected in increased lattice energy. Excellent microwave dielectric properties (ε_r = 16.23, Q × f = 89,728 GHz, τ_f = −43.5 ppm/°C) were obtained for x = 3 ceramic sintered at 1140°C. Even at x = 5, the ceramic retains excellent microwave dielectric properties (ε_r = 16.02, Q × f = 63,079 GHz, τ_f = −26 ppm/°C) at a low sintering temperature of 900°C. This work realizes the multiple effects of LiF and confirms good chemical compatibility with silver for LTCC (low-temperature co-fired ceramics) applications.