Lanthanide L-Edge Spectroscopy of High-Entropy Oxides: Insights into Valence and Phase Stability

TL;DR

This study combines X-ray spectroscopy and DFT calculations to explore how compositional changes in high-entropy oxides affect their electronic structure and phase stability, revealing valence states and phase transition mechanisms.

Contribution

It provides new insights into the relationship between composition, valence states, and phase stability in rare-earth high-entropy oxides using combined experimental and computational methods.

Findings

Phase transition from bixbyite to fluorite with increasing Ce

La and Sm remain trivalent; Ce shows minor Ce 3+ fraction

DFT supports phase transition driven by composition, not redox

Abstract

High-entropy oxides (HEOs) are a promising class of multicomponent ceramics with tunable structural and electronic properties. In this study, we investigate the local electronic structure of rare-earth HEOs in the (Ce, Sm, Pr, La, Y)O2 system using X-ray absorption spectroscopy (XAS). By systematically increasing the Ce concentration, we observe a phase transition from bixbyite to fluorite, tracked by X-ray diffraction (XRD) and corroborated by L-edge XANES analysis of La, Sm, Ce, and Pr. The oxidation states of La and Sm remain trivalent, while Ce exhibits a minor Ce 3+ fraction and Pr shows a consistent mixed-valence state. Density functional theory (DFT) calculations with Bader charge analysis support these findings and reveal that the phase transition is driven by compositional effects rather than cation redox. Our combined experimental and computational approach provides new insights into structure-valence correlations in RE-HEOs and their implications for ionic transport and phase stability.