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

The structure, microwave dielectric properties, and low-temperature sintering behavior of acceptor/donor codoped Li sub(2)TiO sub(3) ceramics [Li sub(2)Ti sub(1-x)(Al sub(0.5)Nb sub(0.5)) sub(x)O sub(3) , x = 0-0.3] were investigated systematically. The x-ray diffraction confirmed that a single-phase solid solution remained within 0 < x less than or equal to 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 super(3+) and Nb super(5+) produced a significant effect on the microstructural morphology. Both microcrack healing and grain growth contributed to the obviously enhanced Qf values. By comparison, the decrease of epsilon sub(r) and tau sub(f) values was ascribed to the ionic polarizability and the cell volume, respectively. Excellent microwave dielectric properties of epsilon sub(r) ~ 2 1.2, Qf ~ 181 800 GHz and tau sub(f) ~ 12.8 ppm/ degree C were achieved in the x = 0.15 sample when sintered at 1150 degree C. After 1.5 mol% BaCu(B sub(2)O sub(5)) additive was introduced, it could be well sintered at 950 degree C and exhibited good microwave dielectric properties of epsilon sub(r) ~ 2 0.4, Qf ~ 53 290 GHz and tau sub(f) ~ 3.6 ppm/ degree 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.