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 [Li2Ti1-x(Al0.5Nb0.5)(x)O-3, x=0-0.3] were investigated systematically. The x-ray diffraction confirmed that a single-phase solid solution remained within 0<x0.2 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 Qxf values. By comparison, the decrease of epsilon(r) and (f) values was ascribed to the ionic polarizability and the cell volume, respectively. Excellent microwave dielectric properties of epsilon(r similar to)21.2, Qxf similar to 181800GHz and (f) similar to 12.8ppm/degrees C were achieved in the x=0.15 sample when sintered at 1150 degrees C. After 1.5mol% BaCu(B2O5) additive was introduced, it could be well sintered at 950 degrees C and exhibited good microwave dielectric properties of epsilon(r)similar to 20.4, Qxf similar to 53290GHz and (f)similar to 3.6ppm/degrees 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.