Effect of Al3+ substitution on the structure and microwave dielectric properties of Mg2SiO4 ceramics
摘要
Magnesium orthosilicate (Mg2SiO4) ceramics typically require high sintering temperatures (> 1400 °C) to achieve full densification, which limits their practical application. In this work, Mg2Si1-0.75xAlxO4 (0 ≤ x ≤ 0.12) ceramics were prepared via a conventional solid-state reaction method using 1.5 wt.% Li2CO3 as a sintering aid. The effects of Al3+ substitution for Si4+ on the sintering behavior, microstructure, and microwave dielectric properties were systematically investigated. The substitution of larger Al3+ (r = 0.535 Å) for smaller Si4+ (r = 0.41 Å) induced local lattice distortion and lowered the activation energy for atomic diffusion, successfully reducing the optimal sintering temperature to 1300 °C. The specimen with x = 0.08 exhibited a dense and uniform microstructure with an average grain size of 0.77 μm and a high bulk density of 3.182 g/cm3. Excellent microwave dielectric properties were achieved: εr = 7.1, Q × f = 130,194 GHz, and τf = −64.58 ppm/°C. The significant enhancement in the Q × f value is ascribed to the combined contribution of suppressed extrinsic losses, achieved through high densification, and the optimization of intrinsic bond strength. However, excessive doping (x ≥ 0.12) led to the formation of an MgAl2O4 secondary phase and abnormal grain growth, which deteriorated the dielectric performance. This study demonstrates that Al3+ substitution is an effective strategy for developing low-temperature sintered, high-performance Mg2SiO4 ceramics for high-frequency communication devices.