Improved microwave dielectric properties of MgAl₂O₄ spinel ceramics through (Li_1/3Ti_2/3)³⁺ doping

Abstract In this work, a series of nominal compositions MgAl2-x (Li1/3Ti2/3) x O4 (x = 0, 0.04, 0.08, 0.12, 0.16 and 0.20) ceramics were successfully prepared via the conventional solid-state reaction route. The phase compositions, microstructures, and microwave dielectric properties were investigated. The results of X-ray diffraction (XRD) and Scanning electron microscopy (SEM) showed that a single phase ceramics of MgAl2-x (Li1/3Ti2/3) x O4 with spinel structure were obtained at x ≤ 0.12, whereas the second phase MgTi2O5 appeared when x > 0.12. The cell parameters were obtained by XRD refinement. As the x values increased, the unit cell volume kept expanding. This phenomenon could be attributed to the partial substitution of (Li1/3Ti2/3)3+ for Al3+. Results showed that (Li1/3Ti2/3)3+ doping into MgAl2O4 spinel ceramics effectively reduced the sintering temperature and improved the quality factor (Qf) values. Optimum microwave dielectric properties were achieved for sample at x = 0.20 sintering at 1500℃ in oxygen atmosphere for 4 h: dielectric constant (εr) = 8.78, temperature coefficient of resonant frequency (τf) = -85 ppm/ ℃, and Qf = 62,300 GHz. The Qf value of x = 0.20 sample was about two times higher than that of pure MgAl2O4 ceramics (31600 GHz). Thus, MgAl2-x (Li1/3Ti2/3) x O4 ceramics with excellent microwave dielectric properties can be applied to 5G communications.