Pressure and temperature dependence of the electronic structure of superconducting (SC) ${\text{CeFeAsO}}_{1-y}$ and non-SC ${\text{CeFeAsO}}_{1-y}$ have been investigated using two complementary hard x-ray spectroscopic probes at the $\text{Ce}{L}_3$ edge, partial fluorescence yield x-ray absorption spectroscopy and resonant x-ray emission spectroscopy. With increasing pressure, the ratio between the intensity of the peak related to the $f^0$ $\left({\text{Ce}}^{4+}\right)$ state and that of the $f^1$ $\left({\text{Ce}}^{3+}\right)$ state, $I\left(f^0\right)/I\left(f^1\right)$, is found to increase continuously for both compounds, indicating a continuous increase in the Ce valence. The valence of non-SC ${\text{CeFeAsO}}_{1-y}$ is found to be slightly higher than that of SC ${\text{CeFeAsO}}_{1-y}$ in the entire pressure and temperature ranges of this study. The valence of ${\text{CeFeAsO}}_{1-y}$ around 6 GPa, where the superconductivity breaks down, is estimated to be $\sim 3.0$, but no change in the valence is observed upon cooling. The dependence of the interatomic distances on the concentration of oxygen vacancies is studied via extended absorption fine structure spectroscopy.

• Received 12 July 2010

DOI:https://doi.org/10.1103/PhysRevB.82.125123