ZnO-doped BaTiO3: Microstructure and electrical properties

In the present work, ZnO additions ranging from 0.1 to 10 wt% to ceramic BaTiO3 have been studied. By means of a controlled processing, two different compounds were tested as a source of ZnO. The dopant distribution plays a key role in the microstructural development of the ZnO-doped BaTiO3. When zinc stearate was used, homogeneous fine-grained microstructure was obtained for 0.1 wt% of ZnO. However, high density was avoided by burn out of the long organic chain. When solid ZnO was used as dopant, homogeneous fine-grained microstructure and density values around 99% D-t (D-t = 6.017 g cm(-3)) were obtained for ZnO compositions starting from 0.5 wt%. The sintering temperature was 100 degrees C lower than for undoped BaTiO3. Control of grain growth in a wide temperature range led to ceramics with permittivity values close to 3000 and dielectric losses well below 1%. The incorporation of Zn2+ cations into the BaTiO3 lattice takes place in Ba2+ sites, i.e. as an isovalent dopant. The solid solubility of ZnO in BaTiO3 was stated to fall below 0.5 wt% in the range of sintering temperatures studied. Additions of large amounts of ZnO led to BaTiO3-ZnO composite materials. (C) 1997 Elsevier Science Limited. All rights reserved.