Phase composition, crystal structure, and microwave dielectric properties of LiIn_1‐xAl_xO₂ ceramics

Abstract

A series of LiIn1‐xAlxO2 (x =0.05, 0.10, 0.15, 0.20, 0.25) microwave dielectric ceramics with low permittivity were synthesized via a solid‐state reaction method. XRD, Raman spectra, and SEM analysis reveal that a single LiInO2 tetragonal structure phase could be obtained at the x < 0.10, and with the x increased further to 0.15–0.25, the diffraction peaks of the secondary phase LiAlO2 were detected. In the LiIn1‐xAlxO2 ceramics, the τf was closely related to the εr, and the relative density, microstructure, and microwave dielectric properties were effectively improved by the Al3+ substitution for In3+. Bond valence theory analysis demonstrates that the Al3+ entered the In3+ site exhibits a strength rattling effect, which is beneficial to the increase of εr. While Al3+ substitution for In3+ simultaneously lowers the average ionic polarizability, resulting in a decrease in εr. A near‐zero τf (0.74 ppm/°C) combined with εr approximately 12.83, Q × f = 58 200 GHz, was obtained in LiIn0.85Al0.15O2 ceramic sintered at 970°C.