Effect of ZnO on the microstructure and electrical properties of WO3–Bi4Ti3O12 ceramics

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 Bi2O3 plays a critical role during sintering. Both Bi2Ti2O7 and Zn2TiO4 secondary phases are stabilized when adding ZnO. Actually, when WO3 and ZnO are incorporated simultaneously to BIT materials, they interact stabilizing the Bi2Ti2O7 phase and avoiding the incorporation of W6+ 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 WO3, suggesting that WO3 does not form a solid solution with BIT. The curve dielectric constant vs temperature also reveals the role played by the Bi2Ti2O7 phase.