Valence change of praseodymium in Pr0.5Ca0.5CoO3 investigated by x-ray absorption spectroscopy

TL;DR

This study uses x-ray absorption spectroscopy to analyze how praseodymium's valence state changes in Pr0.5Ca0.5CoO3 across the metal-insulator transition, revealing a partial oxidation and hybridization in the insulating phase.

Contribution

It provides detailed spectroscopic evidence of praseodymium valence change and hybridization mechanisms in Pr0.5Ca0.5CoO3, a novel insight into its electronic structure.

Findings

Pr valence state changes across the transition

Approximately 15% of Pr3+ oxidizes to Pr4+

Strong 4f-2p hybridization observed

Abstract

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.