Theoretical prediction on mechanical and thermal properties of a promising thermal barrier material: Y₄Al₂O₉

The mechanical and thermal properties of Y₄Al₂O₉ were predicted using a combination of first-principles and chemical bond theory (CBT) calculations. Density functional theory (DFT) computations were performed for the structural, mechanical, and thermal properties, and the results were confirmed by chemical bond theory. Based on the calculated equilibrium crystal structure, heterogeneous bonding nature has been revealed, i.e., Al–O bonds are stronger than Y–O bonds. Low second-order elastic constants c₄₄, c₅₅, and c₆₆ demonstrate the low shear deformation resistance. Low G/B ratio suggests that Y₄Al₂O₉ is a damage tolerant ceramic. Y₄Al₂O₉ shows anisotropy in elastic behavior based on the discussion of direction dependence of Young’s modulus. The hardness is predicted to be 10.2 GPa from calculated elastic moduli. The thermal expansion coefficient (TEC) calculated by chemical bond theory is 7.51×10^-6 K^-1. In addition, the minimum thermal conductivity of Y₄Al₂O₉ is estimated to be 1.13 W·m^-1·K^-1, and the thermal conductivity decreases with temperature as 1305.6/T.