Stability of the Cationic Oxidation States in Pr0.50Sr0.50CoO3 across the Magnetostructural Transition by X-ray Absorption Spectroscopy

The possible hybridization between Pr 4f and O 2p states in Pr0.50Sr0.50CoO3 at low temperatures was investigated by different techniques. First, using neutron diffraction we observed a strong contraction of some Pr-O bonds across the magnetostructural transition at T-S similar to 120 K. In contrast to the Pr-O bond contraction in Pr0.50Ca0.50CoO3, this transition is not accompanied by the appearance of Pr4+ at low temperatures, as revealed by X-ray absorption spectroscopy at Pr edges. Despite the fact that a Pr valence change is not the mechanism that drives this transition, we point out an active participation of Pr ions across T-S. Moreover, Co L-2,L-3-edge and O K edge X-ray absorption spectra did not reveal any spin-state variation and showed the stability of the average formal valence of cobalt ions. The large density of empty t(2g) symmetry states in the studied thermal range does not suggest the occurrence of Co3+ in a pure low-spin state. The overall metallic behavior agrees with our findings. We propose a mixture of Co3+ ions in the intermediate-spin or high-spin configuration together with Co4+ ions in a low- or intermediate-spin state.