Theoretical investigation on radiation tolerance of M_n+1AX_n phases

Ternary M_n+1AX_n phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, M_n+1AX_n materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different M_n+1AX_n (MAX) phases in terms of electronic structure, including the density of states (DOS) and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds, thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between M_n+1AC_n and M_n+1AN_n due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti₃AlC₂ to Ti₂AlC (Ti₃AlC₂ and Ti₂AlC have the same chemical elements), can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other M_n+1AX_n phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.