In this paper we offer an interpretation of the previously observed trend of the electric
field gradient (EFG) values measured in a group of semiconducting delafossites
CuBO2
(B = Al,
Fe, Cr, Nd) at Cd impurities which substitute either Cu or B atoms. Our theoretical study
indicates that this EFG trend reveals one of the most subtle details in the electronic
spectrum of the compounds, namely whether the impurity states are formed within or out
of the band gap. When Cd substitutes the Cu, it exhibits a larger EFG value in
CuAlO2 and
CuFeO2 than
in CuCrO2
and CuNdO2. This occurs because the Cd states form in the first two compounds a shallow band within
the gap, but in the second two compounds they do not. When Cd substitutes the B atom it
exhibits almost the same EFG in all delafossites. In this case, Cd states are not formed within
the gap in any of the compounds. The same interpretation can be applied to the whole family of
CuBO2
delafossites, whatever the B atom is. To arrive at these conclusions we analysed and calculated various systems
(Cd-doped CuAlO2
and CuCrO2
compounds, and molecular clusters) using the full-potential linear augmented plane wave
method.