Structure, Microwave Dielectric Properties, and Low‐Temperature Sintering of Acceptor/Donor Codoped Li 2 Ti 1− x (Al 0.5 Nb 0.5 ) x O 3 Ceramics

The structure, microwave dielectric properties, and low‐temperature sintering behavior of acceptor/donor codoped Li 2 TiO 3 ceramics [Li 2 Ti 1− x (Al 0.5 Nb 0.5 ) x O 3 , 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 Al 3+ and Nb 5+ 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(B 2 O 5 ) 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.