Molecular dynamics simulation of Y-doped (sigma)37 grain boundary in alumina

A molecular dynamics technique with a multi-atom potential was used to simulate the behavior of Y-doping in (sigma)37 grain boundary (GB) in (alpha)-Al2O3. Results on melting process, elastic constants, and GB diffusivity in pure (alpha)-Al2O3, (sigma)37 GB, and Y-doped (sigma)37 GB have been obtained and compared with available experimental data. Our simulation indicates that the pure GB pre-melts at a temperature of 1417 K before the bulk melts at 2105 K. When doped with Y, a melting nucleate around Y is formed and the pre-melting temperature is increased to 1536 K. The diffusivities of Al and O in the GB region have the same order of magnitude. In comparison, Y-doping decreases diffusivity and increases diffusion activation energy of both Al and O at the GB. Our results are consistent with the notion of "siteblocking" effect to explain the decrease in GB diffusivity with Y-doping. At low temperature (<1536 K), "site-blocking" is due to the larger size of Y ions, but at a high temperature (>1536 K), "site-blocking" is related to possible formation of nucleates surrounding the Y ions.