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

A series of nominal compositions MgAl2-x(Li1/3Ti2/3)xO4(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 mi-crowave 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)xO4 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(Qf)values.Good microwave dielectric properties were achieved for a sample at x=0.20 sintering at 1500℃in air for 4 h:dielectric constant εr=8.78,temperature coefficient of resonant frequency τf=-85 ppm/℃,and Qf=62300 GHz.The Qf value of the x=0.20 sample was about 2 times higher than that of pure MgA12O4 ceramics(31600 GHz).Thus,MgAl2-x(Li1/3Ti2/3)xO4 ceramics with excellent microwave dielectric properties can be applied to 5G communications.