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

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Abstract
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 c 44, c 55, and c 66 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.

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