Point Defect Formation in M2AlC (M = Zr,Cr) MAX Phases and Their Tendency to Disorder and Amorphize

First principles calculations are performed on Zr 2 AlC and Cr 2 AlC MAX phases to compare their ability to accommodate point defects under irradiation. Interatomic bonding is stronger in Cr 2 AlC than Zr 2 AlC but contrary to expectation Zr 2 AlC exhibits higher vacancy and antisite pair formation energies. However, interstitials and Frenkel defects are generally more difficult to form in Cr 2 AlC. The results are attributed to the mixed covalent/ionic/metallic nature of the bonding. Detailed comparison of all the energies suggests that the preferred defects in Zr 2 AlC and Cr 2 AlC are the V Al +Al i Frenkel and Cr Al +Al Cr antisite respectively. Thus the potential response of the two phases to irradiation is different and taking account of other competing defects it is suggested that Zr 2 AlC is less susceptible to amorphization.