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

New MAX phases Ti2(AlxCu1−x)N and Nb2CuC were synthesized by A-site replacement by reacting Ti2AlN and Nb2AlC, respectively, with CuCl2 or CuI molten salt. X-ray diffraction, scanning electron microscopy, and atomically resolved scanning transmission electron microscopy showed complete A-site replacement in Nb2AlC, which lead to the formation of Nb2CuC. However, the replacement of Al in Ti2AlN phase was only close to complete at Ti2(Al0.1Cu0.9)N. Density-functional theory calculations corroborated the structural stability of Nb2CuC and Ti2CuN phases. Moreover, the calculated cleavage energy in these Cu-containing MAX phases are weaker than in their Al-containing counterparts. The preparation of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N were realized by A-site replacement in Ti2AlN and Nb2AlN, respectively.Funding agencies: National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21671195, 51902319, 91426304]; Chinese Academy of SciencesChinese Academy of Sciences [2019VEB0008, 174433KYSB20190019]; Swedish Government Strategic Research