Changes induced by the presence of Zn or Ni impurity at Cu sites in CuAlO2 delafossite

A semiconducting delafossite compound CuAlO2 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 CuAlO2 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 dz2 electrons. This effect is responsible for the large difference between the EFG values calculated at the Ni and Zn nuclei in the compound.