GRAIN-GROWTH CONTROL AND DOPANT DISTRIBUTION IN ZNO-DOPED BATIO3

ZnO additions to BaTiO3 have been studied in order to determine the ro le of this dopant on sintering and microstructure development. As a co nsequence of a better initial dopant distribution, samples doped with 0.1 wt% zinc stearate show homogeneous fine-grained microstructure, wh ile 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 redist ributed among the BaTiO3 particles during heating. Since no liquid for mation has been detected for temperatures below 1400 degrees C in the system BaTiO3-ZnO, it is proposed that dopant redistribution takes pla ce by vapor-phase transport and grain boundary diffusion. Shrinkage an d porosimetry measurements have shown that grain growth is inhibited d uring the first step of sintering for the doped samples. STEM-EDX anal ysis revealed that solid solubility of ZnO into the BaTiO3 lattice is very tow, being strongly segregated at the grain boundaries. Grain gro wth control is attributed to a decrease in grain boundary mobility due to solute drag. Because of its effectiveness in controlling grain gro wth, ZnO appears to be an attractive additive for BaTiO3 dielectrics.