Ce Substitution and Reduction Annealing Effects on Electronic States in Pr^sub 2-x^Ce^sub x^CuO^sub 4^ Studied by Cu K-edge X-ray Absorption Spectroscopy

We investigated the Ce substitution and reduction annealing effects on the electronic states at copper sites by Cu K-edge X-ray absorption near-edge structure measurements in Pr2−xCexCuO4+α−δ (PCCO) with varying x and δ (amount of oxygen loss during annealing). Absorption near-edge spectra were modified by Ce substitution and reduction annealing similarly with increasing x and δ. Considering electron doping by Ce substitution, this similarity indicates an increase in electron number at the copper sites due to annealing (nAN). Thus, the total number of electrons is determined by the amount of Ce and O ions. Furthermore, quantitative analyses of the spectra clarified that the number of Cu+ sites, corresponding to the induced electron number by Ce substitution (nCe) increases linearly with x in the as-sintered PCCO (δ = 0), whereas nAN is not exactly equal to 2δ, which is expected from charge neutrality. For each x-fixed sample, nAN tends to exceed 2δ with increasing δ, suggesting the emergence of two types of carrier due to annealing.