Electric-field gradients at Cd-111 in delafossite oxides ABO(2) (A=Ag, Cu; B=Al, Cr, Fe, In, Nd, Y)

The electric-field gradient of In-111(EC)Cd-111 nuclei at cation sites in the delafossites A (B+3O2)-B-+1 have been measured using perturbed angular correlation spectroscopy. The radioactive In-111 tracers were introduced into the samples via ion implantation. The temperature dependence of the electric-field gradient of Cd-111 in the compounds CuFeO2, CuAlO2, CuCrO2, and CuYO2 was measured in the temperature range 14-1073 K, whereas for AgCrO2, AgInO2, and CuNdO2 only measurements at room temperature were carried out. In each substance at least one electric-field gradient with axial symmetry was found and attributed to B sites. The scaling of this electric-field gradient with the cation-oxygen bond length is discussed and compared with predictions of the point-charge model and measurements in binary metal oxides.