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 degreesC for 20 h exhibit dielectric constants k around 37.1 and a QF value of 41,500 GHz, measured at 4 GHz. After annealing, k remains constant. However, the QF value is strongly affected by the annealing process. At 1300 degreesC, annealing has no effect on the quality factor Q. Annealing at temperatures 1225 and 1200 degreesC induce a approximate to 50% decrease of QF values. Intermediate annealing temperatures of 1275 and 1250 degreesC induce a approximate to 25% improvement of QF values. These ceramics were investigated by XRD, SEM and EDS. The matrix phase ZST was observed together with three different secondary phases: TiO2ss, La2/3TiO3 and TiNiO3. Appearance and following diffusion of these secondary phases and other impurities to the ceramic surfaces during annealing can explain the QF behaviour. (C) 2001 Elsevier Science Ltd. All rights reserved.