Liquid‐phase sintering, microstructural evolution, and microwave dielectric properties of Li2Mg3SnO6–LiF ceramics

Abstract

AbstractThe liquid‐phase sintering behavior and microstructural evolution of x wt% LiF aided Li2Mg3SnO6 ceramics (x = 1‐7) were investigated for the purpose to prepare dense phase‐pure ceramic samples. The grain and pore morphology, density variation, and phase structures were especially correlated with the subsequent microwave dielectric properties. The experimental results demonstrate a typical liquid‐phase sintering in LiF–Li2Mg3SnO6 ceramics, in which LiF proves to be an effective sintering aid for the Li2Mg3SnO6 ceramic and obviously reduces its optimum sintering temperature from ~1200°C to ~850°C. The actual sample density and microstructure (grain and pores) strongly depended on both the amount of LiF additive and the sintering temperature. Higher sintering temperature tended to cause the formation of closed pores in Li2Mg3SnO6‐x wt% LiF ceramics owing to the increase in the migration ability of grain boundary. An obvious transition of fracture modes from transgranular to intergranular ones was observed approximately at x = 4. A single‐phase dense Li2Mg3SnO6 ceramic could be obtained in the temperature range of 875°C‐1100°C, beyond which the secondary phase Li4MgSn2O7 (<850°C) and Mg2SnO4 (>1100°C) appeared. Excellent microwave dielectric properties of Q × f = 230 000‐330 000 GHz, εr = ~10.5 and τf = ~−40 ppm/°C were obtained for Li2Mg3SnO6 ceramics with x = 2‐5 as sintered at ~1150°C. For LTCC applications, a desirable Q × f value of ~133 000 GHz could be achieved in samples with x = 3‐4 as sintered at 875°C.