The correlation of U valence states with U-U atomic distance in UPd 2 Cd 20 has been investigated by using X-ray diffraction and high-energy resolution X-ray absorption spectra at the U L 3-edge at high pressures. The results revealed the contraction of lattice constant (~2.7%) and the U valence increase (~0.19) in a pressure range of 0-8 GPa. The amount of U valence variation is much larger than the result of the temperature dependence of ~0.04 from 3 to 300 K. In contrast, small humps were observed at 3-4 GPa in both the compression curve and the valence variation, and the result is expected to the anomalous physical properties although it is probably due to the solidification of the pressure medium. It is proposed the relationship that the U valence increases proportional to the contraction of U-U distance.

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We have measured the Yb 3d 5/2 resonant hard x-ray photoemission spectra at the Yb L 3 edge of YbInCu 4 with the valence transition at T V = 42 K. The L 3 resonance effect in both Yb 2+ and Yb 3+ components in the Yb 3d 5/2 spectra is successfully observed at 70 and 20 K. We find that the feature of their constant initial state (CIS) spectra is described with the Fano profile. The feature of the CIS spectra is almost unchanged across T V .

The electronic structure of Eu(Rh 1-x T x) 2 Si 2 (T = Co, Ir) showing a valence change with temperature has been investigated by means of high-energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS). The Eu L 3-edge HERFD-XAS spectra for Eu(Rh 1-x T x) 2 Si 2 distinctly demonstrate that, due to the improvement of the energy resolution, the intensities of Eu 2+ and Eu 3+ components are dependent on temperature. Each component has additional fine structures, which clearly change above and below the transition temperature. These spectral changes are similar to those for EuNi 2 (Si 1-x Ge x) 2 , but the degree of temperature dependence on energy difference between Eu 2+ and Eu 3+ components is different from EuNi 2 (Si 1-x Ge x) 2. The results of this study suggest that a treatment of the many-body interaction is essential to understanding the valence transition of Eu compounds.