Improved microwave dielectric properties of MgAl2O4 spinel ceramics through (Li1/3Ti2/3)3+ doping

Abstract

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 of MgAl2−x (Li1/3Ti2/3) x O4 ceramics with a spinel structure was obtained at x ≤ 0.12, whereas the second phase of 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 (Q f) values. Good microwave dielectric properties were achieved for a sample at x = 0.20 sintering at 1500 °C in air for 4 h: dielectric constant ε r = 8.78, temperature coefficient of resonant frequency τ f = −85 ppm/°C, and Q f = 62 300 GHz. The Q f value of the x = 0.20 sample was about 2 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.