Kinetic Monte Carlo Simulation of Oxygen Diffusion in Yttrium Monosilicate

Ceramic Matrix Composite (CMC) materials are of interest for use in next-generation turbine engines, offering a number of significant advantages, including reduced weight and high operating temperatures. However, in the hot environment in which such components operate, the presence of water vapor can lead to corrosion and recession, limiting the useful life of the components. Such degradation can be reduced through the use of Environmental Barrier Coatings (EBCs) that limit the amount of oxygen and water vapor reaching the component. Candidate EBC materials include Y and Yb mono- and disilicates. In order to better understand the diffusion of oxygen in such coatings, kinetic Monte Carlo computer simulations are performed for vacancy mechanism oxygen diffusion in Y monosilicate. Oxygen vacancy formation energies and migration barrier energies are computed using density functional theory, showing that all reasonably short migration paths involve relatively large barrier energies. In addition, the vacancy formation energies are relatively large as well, indicating that intrinsic vacancy concentrations will be small, leading to the conclusion that oxygen permeation associated with vacancy-mechanism oxygen diffusion will be small in this material.