Temperature-dependent elastic stiffness constants ofα- andθ-Al2O3 from first-principles calculations

Abstract

Temperature-dependent elastic stiffness constants (cijs), including both the isothermal and isoentropic ones, have been predicted for rhombohedralα-Al2O3 andmonoclinic θ-Al2O3 in terms of a quasistatic approach, i.e., a combination of volume-dependentcijs determined by a first-principles strain versus stress method and direction-dependentthermal expansions obtained by first-principles phonon calculations. A goodagreement is observed between the predictions and the available experiments forα-Al2O3, especially for the off-diagonal elastic constants. In addition, the temperature-dependentcijs predicted herein, in particular the ones for metastableθ-Al2O3, enable the stress analysis at elevated temperatures in thermally grown oxides containingα- andθ-Al2O3, which are crucial to understand the failure of thermal barrier coatings in gas-turbineengines.