Electronic Structure and Mechanical Properties of 20 Max Phase Compounds

A relatively new class of transition metal layered compounds Mn+1AXn, (MAX phases) where M is an early transition metal, A a group A element most likely Al, and X is C or N with n = 1, 2, 3 or 4. Due to their unique structural arrangements and directional bonding, these ternary compounds possess some very outstanding mechanical and chemical properties such as damageresistance, oxidation resistance, excellent thermal and electric conductivity, machinability, and fully reversible dislocation-based deformation. These properties can be explored in the search for new phases and their composites to meet the performance goals of advanced materials with applications in fossil energy conversion technology. Systematic and detailed computational studies on MAX phase compounds can provide fundamental understanding of the key characteristics that lead to these desirable properties and to the discovery of other new and better alloys. In this paper, we present results on the electronic structure and mechanical properties of 20 MAX phase compounds using first-principles methods. They are: Ti3AC2 (A = Al, Si, Ge), Ti2AC (A = Al, Ga, In, Si, Ge, Sn, P, As, S), Ti2AlN, M2AlC (M = V, Nb, Cr), and Tan+1AlCn (n = 1 to 4). The calculated results include: band structures, total and partial density of states, effective charges on each atom, quantitative bond order values, interband optical conductivities, elastic coefficients, bulk modulus, shear modulus, Young’s modulus, Poisson’s and Pugh ratios. By systematically analyzing these results and in comparison with available experimental data, several important features on structural stability, interatomic bonding and optical conductivities are identified. These results form part of the data base that will enable us to explore and predict new MAX phases and new composite alloys with better physical properties as advanced materials for various applications at extreme conditions.