Grain Growth and Twin Formation in 0.74 PMN-0.26 PT
Jay S. Wallace, J M. Huh, J Blendell, C A. Handwerker
The mechanisms controlling normal and exaggerated grain growth in lead magnesium niobate-lead titanate (PMN-PT) ceramics have been investigated by varying the PbO-based liquid phase volume fraction from 0.03 to 0.6 and sintering temperature form 900 C to 1100 C. There was a transition in grain growth rate and grain shape with increasing liquid fraction; samples with liquid volume fractions <0.2 showed relatively small equiaxed grains due to impingement and samples with higher liquid fractions showed significantly larger, facetted, cube-shaped grains, whose size was independent of liquid fraction, indicating a surface nucleation rate controlling growth mechanism. Exaggerated grains were found in the high liquid fractions samples. Orientation imaging microscopy showed that all of the exaggerated grains contained 60 <111> twins whereas none of the normal matrix grains contained twins. The reentrant angles in the twinned grains have them a growth advantage over untwined grains due to the relative ease of nucleating ledges on a facetted surface.