The microstructure and microwave dielectric properties of zirconium titanate ceramics in the solid solution system ZrTiO4-Zr5Ti7O24

Zirconium titanate (ZT) ceramics having compositions in the range of ZrTiO4-Zr5Ti7O24 were prepared via the mixed oxide route, using ZnO and CuO as sintering aids and Y2O3 as stabilizer. Specimens were sintered at 1450 degrees C for 4 h and then cooled at 6 degrees C h(-1), 120 degrees C h(-1) or air-quenched. All products exhibited densities exceeding 95% of the theoretical values. The amount of ZnO and CuO in the products decreased as the cooling rate decreased and as the content of TiO2 increased. Energy dispersive analytical spectroscopy studies suggested that a grain boundary phase, rich in ZnO and CuO, existed as a continuous layer. Both composition and cooling rate were found to have significant effects on the microstructure of the zirconium titanate ceramics. Transmission electron microscopy showed that as the TiO2 content increased, a superstructure with a tripled a-axis developed, but there was no obvious change in the lattice parameters. As the cooling rate decreased, extra peaks were observed in X-ray spectra and the lattice parameter in the b direction shortened dramatically; both are associated with cation ordering. A short-range commensurate superstructure with a Z(TT)ZZ(TT)Z(TT)ZZ(TT) (or Z(TT)ZZ(TT)Z(TT)ZZ(TT)) stacking sequence was observed in the ordered ZrTiO4 specimens. All the samples showed poor dielectric properties at microwave frequency (4 GHz). The low dielectric Q va lues (400-1000) were due to the presence of the structural stabilizer, Y2O3, within the grains. The Q value increased slightly with increasing TiO2 content. The air-quenched samples had the highest Q values (850-1000); slower cooling led to the formation of microcracks within the samples and the reduction of Q values. The relative permittivity was controlled by bulk composition, the presence of a grain boundary phase, microcracks, oxygen vacancies and cation ordering. The ordering of cations and the presence of microcracks reduced the relative permittivity; rapidly cooled samples with higher TiO2 content had higher relative permittivities (with a maximum of 44.3 for air-quenched Zr5Ti7O24).