Abstract
The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti2AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti2AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti2AlC. However, the electrical conductivity of the Ti2AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti2AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti2AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti2AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti2AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti2AlC MAX phase ceramic.
Highlights
The MAX phases, a group of ternary compounds with layered nanostructure, have attracted interest in the field of ceramics in recent 20 years. They have the general formula of Mn+1 AXn (n = 1, 2 or 3), where M belongs to a transition metal, A is an element of group
For the original Ti2 AlC, Ti2 (Al1−x,Agx )C, and (Ti1−y,Agy )2 AlC, the equilibrium lattice parameter and ground-state electronic structure were calculated by adjusting the substitution ratio of Ag for Al and Ti in the supercell
The first-principles calculations were introduced to investigate the influence of Ag substitution for Al or Ti on structure and stability of the Ti2 AlC MAX phase ceramic
Summary
The MAX phases, a group of ternary compounds with layered nanostructure, have attracted interest in the field of ceramics in recent 20 years. They have the general formula of Mn+1 AXn (n = 1, 2 or 3), where M belongs to a transition metal, A is an element of group. It should be mentioned that Ti, Al, and C atoms in the Ti2 AlC lattices can be substituted by other atoms [11,12,13,14,15,16,17,18,19]. Compared to the Ti2 AC, the Vickers hardness, flexural, and shear strength of the (Ti0.8 ,V0.2 ) AlC were enhanced by 29%, 36%, and 45%, respectively
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