The effects of Fe, Co and Ni doping in CuAl2O4 spinel surface and bulk: A DFT study

Abstract

The effects of the substitution of Al and Cu by transition metal (Fe, Co and Ni) in CuAl2O4 spinel were investigated by density functional theory (DFT). The results show that the incorporation of Fe, Co and Ni into the Al and Cu sites of the CuAl2O4 spinel is thermodynamically feasible. It has been found that Ni prefers to locate in the octahedral sites in spinel surface as well as in bulk, while Fe and Co prefer to locate in the tetrahedral sites of the spinel in the surface layers, vs. in the octahedral sites in spinel bulk. Bader charge and partial density of states (PDOS) analysis reveal that Fe, Co and Ni substitution for Cu and Al site of CuAl2O4 spinel surface is accompanied by charge transfer. The order of charge transfer from Fe, Co and Ni to the spinel surface capability is Fe > Co > Ni. In addition, the (1 0 0) surface of CuAl2O4 spinel has stronger ability than the (1 1 0) surface to get electrons from Fe, Co and Ni. As indicated by PDOS, new peaks emerged above the Fermi level due to the empty orbitals of the positively charged Fe, Co and Ni resulting that the doped CuAl2O4 has narrower band gap than that of CuAl2O4 spinel surface.