Effect of ZnO on the microstructure and electrical properties of ceramics

摘要

The aim of the present work is to explore the possibility of incorporate a small amount of ZnO to improve the microstructure control of W-doped BIT-based materials. Two different processing routes have been used according to previous results reported for other materials: reaction and sintering in one single step and a previous calcination step. The sintering behaviour of the samples, the obtained crystalline phases and the microstructure analysis indicate that the reaction between ZnO and Bi_2O_3 plays a critical role during sintering. Both Bi_2Ti_2O_7 and Zn_2TiO_4 secondary phases are stabilized when adding ZnO. Actually, when WO_3 and ZnO are incorporated simultaneously to BIT materials, they interact stabilizing the Bi_2Ti_2O_7 phase and avoiding the incorporation of W~(6+) into the BIT lattice. As a consequence, the electrical conductivity of the samples with ZnO is two orders of magnitude higher than that of the samples doped only with WO_3, suggesting that WO_3 does not form a solid solution with BIT. The curve dielectric constant vs temperature also reveals the role played by the Bi_2Ti_2O_7 phase.