Ce-doping and reduction annealing effects on electronic states in Pr$_{2-x}$Ce$_{x}$CuO$_4$ studied by Cu ${K}$-edge X-ray absorption spectroscopy

We investigated 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 Pr$_{2-x}$Ce$_x$CuO$_{4+alpha-delta}$ (PCCO) with varying $x$ and $delta$ (the amount of oxygen loss during annealing) values. Absorption near-edge spectra were modified by Ce-substitution and reduction annealing in a similar manner with increasing $x$ and $delta$. Considering electron doping by Ce-substitution, this similarity indicates an increase of electron number at the copper sites due to annealing $n_{rm AN}$. Thus, the total number of electrons is determined by the amount of Ce and oxygen ions. Furthermore, quantitative analyses of the spectra clarified that the number of Cu$^+$ sites, corresponding to the induced electron number by Ce-substitution $n_{rm Ce}$ increases linearly with $x$ in the as-sintered PCCO ($delta=0$), whereas $n_{rm AN}$ is not exactly equal to twice of $delta$, which is expected from charge neutrality. For each $x$-fixed sample, $n_{rm AN}$ tends to exceed 2$delta$ with increasing $delta$, suggesting the emergence of two types of carrier due to annealing.