Paper detail

The theoretical prediction of multifunctional Nb4AC3 (A=Al, Si,Ga, Ge): potential superconductors and unconventional optical properties

Three new phases of ternary transitional metal carbides, namely MAX phases, Nb4SiC3, Nb4GeC3 and Nb4GaC3 were proposed by means of density functional theory, and they were all predicted to be mechanically stable. It was figured out that the alpha type crystal structures of the hypothesized nanolaminates are energetically favored than beta type. Together with the known Nb4AlC3, the role of A group elements in Nb4AC3 (A= Al, Si, Ga, Ge) on various properties were systematically investigated. Not only bulk moduli, compressibility, shear moduli, and Youngs moduli, but the approach to the ductility was discussed and raised as that the ductility can be achieved by forming Nb4AC3 containing more heavier p electrons. All the studied Nb4AC3 phases exhibit the metallic nature that results from the Nb-4d states being dominant at the Fermi level. The typical 4d-2p hybridization between Nb-C leads to strong covalent bond and the contribution from the weaker 4d-3p(4p) hybridization between Nb-A are also identified. The p electrons in A elements can effectively alter the covalency and the iconicity of the bonds that govern the compressibility, ductility and even superconductive properties. The extremely high population at the Fermi level in the density of states and the nesting effects in the Fermi surface shown in Nb4SiC3 both bring this material to a potential superconductor. The regular anisotropic behavior in the dielectric function is present but not in Nb4SiC3. Furthermore, Nb4GeC3 was also predicted to be a very promising candidate solar heating barrier material. The present work gives insight to the role of A elements on the mechanical, superconducting and optical properties of Nb4AC3 phases, and the obtained tendency by changing A elements will fertilize the desirable materials design of functional ceramics.