Changes induced by the presence of Zn or Ni impurity at Cu sites in CuAlO 2 delafossite

Abstract

A semiconducting delafossite compound CuAlO 2 containing either Zn or Ni impurity substituting for a Cu position has been investigated. The electronic structure and the electric field gradients (EFGs) for both donor (Zn) and acceptor (Ni) doped systems have been calculated using a full potential linear augmented plane-wave method with generalized gradient approximation accounting for the exchange and correlation effects. The results clearly indicate that the presence of Zn impurities changes the electric properties of CuAlO 2 by producing n-type semiconductivity, in a similar way as we have previously shown for the Cd impurity. In the case when Ni substitutes Cu the results of calculations indicate p-type semiconductivity in the material. Despite the fact that both Zn and Ni exhibit a similar hybridization scheme for the bonding with neighboring oxygens, their d electron clouds have different shapes due to deficit (Ni) and excess (Zn) of the d z 2 electrons. This effect is responsible for the large difference between the EFG values calculated at the Ni and Zn nuclei in the compound.