Investigation on the bond characteristics and microwave dielectric properties of rock salt-structured Li2Mg0.5nTiO3+0.5n (n = 1–8) ceramics based on the complex chemical bond theory

Abstract

Cubic rock salt structured ceramics are of great interest due to their outstanding microwave dielectric properties. Complex chemical bond theory and polarization theory combined with XRD refinement as well as XPS were employed to reveal the mechanisms of the compositional effect on the microwave dielectric properties of Li2Mg0.5nTiO3+0.5n ceramics with a rock salt structure. It was demonstrated that when n = 1, the microwave dielectric properties exhibit a biphasic structure. However, as n increased to 2 and higher levels, the specimens were consisted of a single cubic rock salt phase. εr of single-phased samples decreased with an increase in the n value, which was due to the decreases in both the bond ionicity and polarizability of unit cell. Meanwhile, as lattice energy increased, the formation of oxygen vacancies was effectively suppressed, and anharmonic lattice vibrations were weakened, leading to an increase in Q×f. Moreover, τf showed a negative shift due to an increase in the aL,ave of the chemical bond and an decrease in the bond energy. The optimal microwave dielectric properties of εr= 17.3, Q×f= 81,000 GHz, and τf = −7.7 ppm/℃ were achieved in the component with n = 1 when sintered at 1350 °C for 4 h.