Valence change of praseodymium in Pr0.5Ca0.5CoO3 investigated by x-ray   absorption spectroscopy
  X-ray absorption spectroscopy measurements in Pr0.5Ca0.5CoO3 were performed at the Pr M4,5, Pr L3, and Ca L2,3 absorption edges as a function of temperature below 300 K. Ca spectra show no changes down to 10 K while a noticeable thermally dependent evolution takes place at the Pr edges across the metal-insulator transition. Spectral changes are analyzed by different methods, including multiple scattering simulations, which provide quantitative details on an electron loss at Pr 4f orbitals. We conclude that in the insulating phase a fraction [15(+5)%] of Pr3+ undergoes a further oxidation to adopt a hybridized configuration composed of an admixture of atomic-like 4f1 states (Pr4+) and f- symmetry states on the O 2p valence band (Pr3+L states) indicative of a strong 4f- 2p interaction. 
J. Herrero-Mart\'in, J. L. Garc\'ia-Mu\~noz, S. Valencia, C. Frontera,   J. Blasco, A.J. Bar\'on-Gonz\'alez, G. Sub\'ias, R....
cond-mat.str-el