Point defect formation in M(2)AlC (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.