First principles calculations are performed on Zr₂AlC and Cr₂AlC MAX phases to compare their ability to accommodate point defects under irradiation. Interatomic bonding is stronger in Cr₂AlC than Zr₂AlC but contrary to expectation Zr₂AlC exhibits higher vacancy and antisite pair formation energies. However, interstitials and Frenkel defects are generally more difficult to form in Cr₂AlC. 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 Zr₂AlC and Cr₂AlC 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 Zr₂AlC is less susceptible to amorphization.The calculations were performed at the Cambridge HPCS and the UK National Supercomputing Service, ARCHER. Access to the latter was obtained via the CaFFE consortium and funded by EPSRC under Grant No. EP/M018768/1
