Multiple grain boundary transitions in ceramics: A case study of alumina

There is a growing body of the literature that suggests that there are grain boundary structures that exist in ceramic systems that are not predicted by bulk thermodynamics. Transitions between the various grain boundary structures are not well understood either experimentally or theoretically. This study identifies six different types of grain boundary structures present in the alumina system. These grain boundary structures were directly correlated with significantly different grain boundary mobilities. There is a general trend towards increasing grain boundary disorder and increasing grain boundary mobility with increasing temperature. This is the first time such a broad range of behavior has been observed in a single system. The results have many implications on understanding grain boundary transport phenomena in ceramic systems. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.