Grain Growth Control and Dopant Distribution in ZnO‐Doped BaTiO₃

Abstract

ZnO additions to BaTiO 3 have been studied in order to determine the role of this dopant on sintering and microstructure development. As a consequence of a better initial dopant distribution, samples doped with 0.1 wt% zinc stearate show homogeneous fine-grained microstructure, while a doping level of 0.5 wt% solid ZnO is necessary to reach the same effect. When solid ZnO is used as the dopant precursor, ZnO is redistributed among the BaTiO 3 particles during heating. Since no liquid formation has been detected for temperatures below 1400°C in the system BaTiO 3 -ZnO, it is proposed that dopant redistribution takes place by vapor-phase transport and grain boundary diffusion. Shrinkage and porosimetry measurements have shown that grain growth is inhibited during the first step of sintering for the doped samples. STEM-EDX analysis revealed that solid solubility of ZnO into the BaTiO 3 lattice is very low, being strongly segregated at the grain boundaries. Grain growth control is attributed to a decrease in grain boundary mobility due to solute drag. Because of its effectiveness in controlling grain growth, ZnO appears to be an attractive additive for BaTiO 3 dielectrics.

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