Reduction and oxidation annealing effects on Cu K-edge XAFS for electron-doped cuprate superconductors

摘要

Reduction and oxidation annealing effects on the electronic states around the copper sites for Pr_(2-x)Ce_xCuO_4 and Nd_(2-x)Ce_xCuO_4 with x = 0 and x = 0.15 were investigated by Cu K-edge x-ray absorption measurements. Cu K near-edge spectra were changed by the reduction annealing in a manner similar to the case of Ce substitution for both x = 0 and x = 0.15. This means an increase of electron density at the copper sites, indicating the aspect of electron doping in the reduction annealing. This reduction annealing effect on the near-edge spectra are reverted by the additional oxidation annealing. The amount of electron density around the copper sites is varied by the reduction and oxidation annealing, reversibly, corresponding to the reversible variation of the physical property from insulating to superconductivity.