ZnO-doped BaTiO₃: Microstructure and electrical properties

Abstract

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 finegrained 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 °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.