Electronic, optical, structural, and elastic properties of MAX phases and (Cr2Hf)2Al3C3

he term "MAX phase" refers to a very interesting and important class of layered ternary transition-metal carbides and nitrides with a novel combination of both metal- and ceramic-like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. In the present dissertation work, the electronic structure and optical conductivities of 20 MAX phases Ti3AC2 (A = Al, Si, Ge), Ti2AC (A = Al, Ga, In, Si, Ge, Sn, P, As, S), Ti2AlN, M2AlC (M = V, Nb, Cr), and Tan+1AlC n (n = 1 to 4) are studied using the first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method. It is confirmed that the N(Ef) (total density of states at the Fermi level Ef) increases as the number of valence electrons of the composing elements increases. The local feature of total density of states (TDOS) near Ef is used to predict structural stability. The calculated effective charge on each atom shows that the M (transition-metal) atoms always lose charge to the X (C or N) atoms, whereas the A-group atoms mostly gain charge but some lose charge. Bond order values are obtained and critically analyzed for all types of interatomic bonds in the 20 MAX phases. Also included in this work is the exploration [using (Cr2Hf)2Al3C3 as an example] of the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of (Cr2Hf)2Al 3C3 are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry ( P63/mmc,...