Structures and mechanical properties of Fe- and Cr-incorporated β-Si5AlON7: First-principles study

The incorporation of Fe and Cr atoms into β-Si5AlON7 and the effects on the mechanical properties of β-Si5AlON7 were theoretically studied at the GGA-PBE/USP level of theory. The incorporation of Fe and Cr atoms shows remarkable site preferences in β-Si5AlON7. The binding energies between the incorporated Fe/Cr atoms and the parent β-Si5AlON7 are ~5.0 eV, indicating both Fe@β-Si5AlON7 and Cr@β-Si5AlON7 are thermodynamically stable. Fe incorporation at the A, B and G sites induces remarkable increase in the shear modulus and Young's modulus; all other Fe/Cr incorporated β-Si5AlON7 structures exhibit lowered shear modulus and Young's modulus than the parent β-Si5AlON7. Except CrG@β-Si5AlON7, the Poisson's ratio of β-Si5AlON7 decreases in all cases of Fe and Cr incorporation.