Ultra-low εr in LiAlSiO4 microwave ceramics with Li excess

Abstract

Li_(1+x)AlSiO₄ ceramics were synthesized using the conventional solid-state reaction method. X-ray diffraction analysis indicated that they crystallized in single-phase hexagonal structure. Li loss was studied using the thermogravimetric-differential scanning calorimetry (TG-DSC). Appropriate excess Li resulted in sintering temperature reduction from 1325 ℃ to 1225 ℃. The ultra-low dielectric constant (ε_r) was influenced by the polarizability per unit volume. Theoretical calculations manifested that enhancing the packing fraction suppressed lattice vibrations, resulting in a significant increase in the quality factor (Q×f). Compared with the pure phase samples, adding Li ions optimized the thermal stability of the ceramics. Specifically, Li_1.02AlSiO₄ demonstrated optimal microwave dielectric properties with ε_r=4.13, Q×f=45,387 GHz and τ_f=-35.54 ppm/°C, making it a spacious application prospect in the field of 6 G communication.