# Influence of Pr Content on Structural Evolution of Doped Ceria-Based High-Entropy Oxides

## TL;DR

This study explores how adding praseodymium (Pr) affects the structure and photocatalytic performance of a high-entropy oxide material.

## Contribution

The novel contribution is the systematic investigation of Pr content's influence on structural evolution and photocatalytic efficiency in doped ceria-based high-entropy oxides.

## Key findings

- Increasing Pr content leads to lattice expansion and microstrain due to Pr³⁺ ion substitution.
- Optimized Pr-doped composition achieved nearly 100% methylene blue degradation under UV light in 30 minutes.
- Pr and Ce redox couples enable efficient charge separation and enhanced photocatalytic performance.

## Abstract

High-entropy fluorite oxides offer exceptional tunability of structure and functionality through controlled multi-cation substitution. In this work, Ce-Zr-Pr-Sm-Eu-based high-entropy oxides, with systematically varied Pr content, were synthesized using a modified sol–gel citrate method to investigate the influence of Pr incorporation on lattice structure, defect formation, and photocatalytic performance. All compositions crystallized in a single-phase cubic fluorite structure, where increasing Pr concentration induced gradual lattice expansion and microstrain due to the substitution of larger Pr3+ ions. Morphological and surface analyses revealed porous nanostructures at moderate Pr levels, while excessive Pr promoted densification and reduced surface accessibility. Spectroscopic studies confirmed the coexistence of Pr3+/Pr4+ and Ce3+/Ce4+ redox couples, strong 4f–2p orbital hybridization, and enhanced defect-related electronic states that narrowed the optical bandgap. The optimized Pr-doped composition exhibited almost 100% degradation of methylene blue under UV light over 30 min, untypical for semiconductors with a narrower bandgap, and is enabled by efficient charge separation and redox cycling between Ce and Pr centers.