First-principles elastic constants of α- And θ- Al ₂O₃

Using an efficient strain-stress method, the first-principles elastic constants cij 's of α - Al2 O3 and θ- Al2 O3 have been predicted within the local density approximation and the generalized gradient approximation. It is indicated that more accurate calculations of cij 's can be accomplished by the local density approximation. The predicted cij 's of θ- Al2 O3 provide helpful guidance for future measurements, especially the predicted negative c15. The present results make the stress estimation in thermally grown oxides containing of α - and θ- Al2 O3 possible, which in turn provide helpful insights for preventing the failure of thermal barrier coatings on components in gas-turbine engines.