Electronic structure and optical properties of layered ternary transition-metal carbides and nitrides

The electronic structure and optical properties of Ti3AC 2 (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∼4) have been studied using first--principles orthogonalized linear combination of atomic orbitals (OLCAO) method. These layered ternary transition--metal carbides and nitrides are also commonly referred to as "MAX phases".;Trends were observed for the calculated density of states (DOS) at Fermi--level, with respect to elemental variations and number of M and X layers. A local minimum of DOS(Ef) was found for Ti3AlC2, Ti2InC and Cr2AlC, predicting relatively high intrinsic structural stability. While a local maximum or an incline was discovered for Ti3GeC2, Ti2GeC, Ti2SnC, Ti 2PC, Nb2AlC, Ta2AlC, Ta4AlC3 and Ta5AlC4, indicating their lower intrinsic structural stability. Inter-band optical conductivities showed anisotropy, but not considerable. The reflectance and colors of the MAX phase compounds were also obtained.