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.
First-principles analysis of cation segregation at grain boundaries in alpha-Al2O3
Fabris, Stefano;
2003-01-01
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 (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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
