Structure,Microwave Dielectric Properties,and Low‐Temperature Sintering of Acceptor/Donor Codoped Li2Ti1−x(Al0.5Nb0.5)xO3 Ceramics

The structure, microwave dielectric properties, and low‐temperature sintering behavior of acceptor/donor codoped Li₂TiO₃ ceramics Li₂Ti_1?x(Al_0.5Nb_0.5)_xO₃, x = 0–0.3] were investigated systematically. The x‐ray diffraction confirmed that a single‐phase solid solution remained within 0 < x ≤ 0.2 and secondary phases started to appear as x > 0.2, accompanied by an order–disorder phase transition in the whole range. Scanning electron microscopy observation indicated that the complex substitution of Al³⁺ and Nb⁵⁺ produced a significant effect on the microstructural morphology. Both microcrack healing and grain growth contributed to the obviously enhanced Q×f values. By comparison, the decrease of ε_r and τ_f values was ascribed to the ionic polarizability and the cell volume, respectively. Excellent microwave dielectric properties of ε_r ~ 21.2, Q×f ~ 181 800 GHz and τ_f  ~ 12.8 ppm/°C were achieved in the x = 0.15 sample when sintered at 1150°C. After 1.5 mol% BaCu(B₂O₅) additive was introduced, it could be well sintered at 950°C and exhibited good microwave dielectric properties of ε_r ~ 20.4, Q×f ~ 53 290 GHz and τ_f ~ 3.6 ppm/°C as well. The cofiring test of the low‐sintering sample with Ag powder proved its good chemical stability during high temperature, which enables it to be a promising middle‐permittivity candidate material for the applications of low‐temperature cofired ceramics.