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 (10 (1) over bar0), the rhombohedral Sigma7 (10 (1) over bar2), and the pyramidal Sigma13 (10 (1) over bar4) twins), three impurities X (X = Se, Y, and La), and two concentrations for the segregant ( approximate to3 and approximate to6 atoms/nm(2)). A partial covalent character is found to be a distinctive feature of the X-O bonds in both bulk and interfacial atomic environments, and to drive the structural distortions of the octahedral XO6 clusters. The energetics of segregation reveals a linear relationship between segregation energy and impurity size. This is interpreted as resulting from a stress field localized at the interface. (C) 2002 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.
|Titolo:||First-principles analysis of cation segregation at grain boundaries in alpha-Al2O3|
|Autori:||Fabris S; Elsasser C|
|Data di pubblicazione:||2003|
|Digital Object Identifier (DOI):||10.1016/S1359-6454(02)00270-7|
|Appare nelle tipologie:||1.1 Journal article|