Insights into the physical properties of a new 211 MAX phase Nb2CuC.

A systematic density functional theory study with two functionals –generalized gradient approximation (GGA) and local density approximation (LDA)–is carried out to explore the structural, electronic, elastic, thermal, vibrational and optical properties of a new 211 MAX phase Nb 2 CuC. To facilitate comparison we also study Nb 2 AlC, the precursor of Nb 2 CuC. The calculated band structures reveal the metallic conductivity of both compounds. The replacement of Al with Cu modifies the band profiles of Nb 2 CuC and consequently leads to its improved physical properties. Considering the position of the Fermi level on the total density of states (DOS), the new compound Nb 2 CuC is structurally less stable than Nb 2 AlC. The total DOS at the Fermi level obtained with GGA is slightly larger than those obtained with LDA. The Nb–C and Nb–A (A = Cu/Al) are covalent bonds, and Nb–Nb bonds lead to antibonding states in both MAX phases. The charge transfer among constituent atoms indicates some ionic character in the chemical bonds of Nb 2 CuC and Nb 2 AlC. Both MAX phases are mechanically and dynamically stable. The Nb 2 CuC is ductile and consequently damage tolerant, whereas Nb 2 AlC is brittle. However, Nb 2 CuC is relatively soft and machinable. In most cases Nb 2 CuC is more elastically anisotropic than Nb 2 AlC, and Nb 2 CuC is expected to be a promising thermal barrier coating material. We propose that Nb 2 CuC is a better coating material for preventing solar heating than Nb 2 AlC, and Nb 2 CuC is expected to be superconductive because its Fermi surface has a nesting nature. Image 1 • Nb 2 CuC is ductile and consequently damage tolerant. • Nb 2 CuC is relatively soft, machinable and elastically more anisotropic than Nb 2 AlC. • Nb 2 CuC is expected to be a promising thermal barrier coating material. • Nb 2 CuC is expected to be a superconductor. [ABSTRACT FROM AUTHOR]