X-RAY-DIFFRACTION DETERMINATION OF THE NI-DOPANT SITE IN SINGLE-CRYSTAL YBA2CU3O7-DELTA

Anomalous dispersive x-ray-diffraction measurements have determined th e dopant-site distribution in Ni-doped single, crystals of the high-te mperature superconductor YBa2Cu3O7-delta. The data from a YBa2[Cu0.83N i0.17]3O7-delta crystal show that over 95% of the Ni dopants occupy th e Cu(2) site in the copper oxide planes, with negligible occupation of the Cu(1) copper oxide chain sites. General guidelines are presented for selecting the most effective hkl diffraction planes for measuring dopant concentration profiles. Direct measurement of the energy depend ence of the dopant atomic scattering factors is also demonstrated.