Effect of annealing on the microwave properties of (Zr, Sn)TiO4 ceramics

(Zr,Sn)TiO4 dielectric ceramics containing La2O3 and NiO as sintering aids were prepared by the conventional solid-state reaction. Ceramics sintered at 1370 C for 20 h exhibit dielectric constants k around 37.1 and a QF value of 41500 GHz, measured at 4 GHz. After annealing, k remains constant. However, the QF value is strongly affected by the annealing process. At 1300 C, annealing has no effect on the quality factor Q. Annealing at temperatures 1225 and 1200 C induces an approximately 50% decrease of QF values. Intermediate annealing temperatures of 1275 and 1250 C induce an approximately 25% improvement of QF values. The matrix phase ZST was observed together with three different secondary phases: TiO2ss, La2/3TiO3 and TiNiO3. Diffusion of these secondary phases and other impurities to the ceramic surfaces during annealing can explain the QF behaviour. 5 refs.