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2003
Journal Article
Titel
First-principles analysis of cation segregation at grain boundaries in alpha-Al2O3
Abstract
The modifications in atomistic structure, chemical bonding, and energetics induced by substitutional cation impurities isolated in the bulk volume and segregated at grain boundaries of alpha-Al2O3 were investigated by combining empirical ionic-model and first-principles electronic-structure calculations. The dependency of these modifications on the boundary type, species and concentration of impurities, was studied by selecting the following variety of systems: three twin boundaries (the prismatic Sigma3 (1010), the rhombohedral Sigma7 (1012), and the pyramidal Sigma13 (1014)twins), three impurities X (X = Sc, Y, and La) , and two concentraitons for the segregant (about 3 and about 6 atoms/nm2). A partial covalent character is found to be a distinctive feature of the X-O bonds in both bulk and interfacial atomic enviroments, and to drive the structural distortions of the octahedral XO6 clusters. The energetics of segregation relveals a linear relationship between segregation energy and impurity size. This is interpreted as resulting from a stress field localized at the interface.