Theoretical predictive screening of noble-metal-containing M3AuC2 (M = Ti, V, and Cr) MAX phases

Abstract

Using first-principles density functional theory (DFT), the ground state physical properties of the newly synthesized noble-metal-containing Ti3AuC2 MAX phase have been investigated. The effect of transition-element Ti replacement (V and Cr) on physical properties, including structural, elastic, electronic, thermal, and optical are presented. The optimized lattice parameters of Ti3AuC2 MAX phase are in good agreement with the experimental values and decrease when we replace Ti with V and then Cr. The magnetic properties of M3AuC2 are predicted by using generalized gradient approximation (GGA) incorporating onsite electron correlation parameter (Hubbard U parameter) within DFT. Out of three studied MAX phases, V3AuC2 and Cr3AuC2 phases exhibit magnetism. The thermodynamical stability of M3AuC2 (M = Ti, V, and Cr) phases is discussed by the formation enthalpy with respect to their most competing phases. The electronic structure reveals that these phases have metallic nature and are electrically anisotropic. The M−element replacement has an effect on the bonding properties of M3AuC2. The bonding between M−C is in the order of Cr3AuC2 > V3AuC2 > Ti3AuC2 according to their peak positions and heights of density of states in the occupied site, which is also confirmed from the charge density distribution. The elastic properties indicate that M3AuC2 phases are ductile, machinable, less stiff, and better resistant to thermal shock and are elastically anisotropic. To understand the properties of M3AuC2 for the extreme environment, we employed a quasi-harmonic Debye model at the pressure and temperature range of 0–50 GPa and 0–1600 K, respectively. Additionally, we evaluated thermal conductivity and melting temperature to further understand the potential of these MAX phases in coating applications at elevated temperature. In relation to optical properties, these MAX phases have a reasonable absorption coefficient in the visible as well as in the ultra-violet regions. The reflectivity of M3AuC2 phases is polarization dependent and of 45 % against the visible region, which reveals its potential as coating material to minimize solar heating.