Structure and microwave dielectric properties of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 ceramics

Aiming to establish relationships between intrinsic structure factors and dielectric characteristics, a series of Li₂Mg₃Ti_1-x(Al_1/2Nb_1/2)_xO₆ (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20) ceramics were synthesized to investigate the influences of (Al_1/2Nb_1/2)⁴⁺ substitution on the dielectric properties of Li₂Mg₃TiO₆ ceramics. The XRD and SEM results revealed that the pure rock salt phase (space group: Fm-3m) with a dense microstructure could be obtained with increasing the (Al_1/2Nb_1/2)⁴⁺ concentration, which is accompanied by an increase in the grain size from 11.69 to 22.81 μm. Meanwhile, some intrinsic factors, such as the average ionic polarizability, bond energy, packing fraction and lattice energy were calculated according to the complex chemical bond theory and refinement results. The unusual change in the dielectric constant (ε_r) was explained by the combined effects of the average ionic polarizability and relative density. The variation in the quality factor (Q × f) was ascribed to the packing fraction and lattice energy. The temperature coefficient of the resonant frequency (|τ_f|) reduced gradually with the increase in the octahedral bond energy, which enhanced the system thermal stability. Particularly, the Li₂Mg₃Ti_0.92(Al_1/2Nb_1/2)_0.08O₆ sample exhibited outstanding dielectric characteristics:ε_r = 15.256, Q × f = 174,300 GHz and τ_f = −19.97 ppm/°C.