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

TL;DR

This study uses Cu K-edge X-ray absorption spectroscopy to analyze how Ce-doping and reduction annealing influence the electronic states in Pr$_{2-x}$Ce$_x$CuO$_{4+eta- ho}$, revealing the relationship between electron doping, oxygen loss, and electronic structure.

Contribution

It provides a detailed quantitative analysis of how Ce-substitution and reduction annealing affect the electron states at copper sites in PCCO, highlighting the emergence of multiple carrier types.

Findings

Electron doping increases linearly with Ce content.

Annealing-induced electron number exceeds twice the oxygen loss, indicating multiple carrier types.

Total electron count depends on Ce content and oxygen loss.

Abstract

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.