Synthesis of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N by A-site replacement reaction in molten salts

摘要

New MAX phases Ti_(2)(Al_(x) Cu_(1?x ))N and Nb_(2)CuC were synthesized by A-site replacement by reacting Ti_(2)AlN and Nb_(2)AlC, respectively, with CuCl_(2) or CuI molten salt. X-ray diffraction, scanning electron microscopy, and atomically resolved scanning transmission electron microscopy showed complete A-site replacement in Nb_(2)AlC, which lead to the formation of Nb_(2)CuC. However, the replacement of Al in Ti_(2)AlN phase was only close to complete at Ti_(2)(Al_(0.1)Cu_(0.9))N. Density-functional theory calculations corroborated the structural stability of Nb_(2)CuC and Ti_(2)CuN phases. Moreover, the calculated cleavage energy in these Cu-containing MAX phases are weaker than in their Al-containing counterparts.