Ab initio study of a Y-doped Σ31 grain boundary in alumina

The atomic structures and energetics of clean and Y-doped general grain boundary (GB) Sigma 31/(0001) models in alpha-Al2O3 are studied by a series of high precision ab initio calculations. A large supercell with 700 atoms and periodic boundary conditions is adopted for undoped and Y-doped GB with different substitution sites and concentrations. It is shown that Y atoms preferably segregate to the central column of the 7-member Al ring. This is explained as more favorable bond formation for Y in this position and lower GB energy. The calculated GB formation energy for the clean and Y-doped cases is respectively 3.99 and 3.67 J/m(2). On the average, the GB region in Sigma 31 has a slightly lower charge density than the bulk crystalline region. In addtition, the GB induces a long ranged asymmetric electrostatic potential distribution on each side of the grain boundary.