Structural Stability, Electronic and Optical Properties of Ni-Doped Boron Carbide by First Principles Calculation

The wide band gap, temperature stability, high resistivity, robustness of semiconducting boron carbide make it an attractive material for device applications.. Here the structural stability along with the electronic and the optical properties of Ni-doped boron carbides (B13C2) were studied using the first principle calculations based on plane wave pseudo-potential theory. The calculated results showed that Ni-doped in boron carbide was in preference to substituting C atom on the end of C-B-C chain, but it was difficult for Ni to substitute B atom in the center of the C-B-C chain or in the icosahedron. A representative stable structural unit containing Ni atom was [C-B-Ni] (epsilon+)-[B11C] (epsilon-), while the structural unit without Ni was [C-B-C] (epsilon-)-[B-12] (epsilon+). The band structure, density of states (DOS) indicated that the coexistence of [C-B-Ni] (epsilon+)[B11C] (epsilon-) structural unit made electrical conductivity increased. Some new impurity energy levels appear in the band gap of Ni-doped B13C2, which can improve the conductivity of B13C2 as well. Ni acts as a n-type dopant. As the covalent bond of Ni-B was weaker than those of B-B and B-C, the thermal conductivity decreased for Ni-doped B13C2, thermoelectric property of Ni-doped boron carbides has been improved. The imaginary part of the dielectric function of Ni-doped B13C2 has three remarkable peaks at 1.13, 3.89, and 6.05 eV. This reveals that doping with Ni can improve the photo-absorption efficiency of B13C2.