Effect of Mg-substitution on the electronic structure, splitting, and optical transitions of Cr2O3 nanoparticles

Abstract

The present study investigates the influence of Mg-substitution on the electronic structure of Cr2O3 nanoparticles using X-ray absorption spectroscopy (XAS) and UV-Vis spectroscopy. Pristine Cr2O3 and Mg-substituted Cr2O3 nanoparticles (with Mg-content varying from x = 0.01 to 0.05) were synthesized using the co-precipitation technique and characterized using X-ray absorption near-edge structure (XANES) at the O K-edge, Cr L2,3-edge, and Cr K-edge. XAS results revealed significant changes in the electronic structure of Cr2O3 upon Mg incorporation, including modifications in the oxidation state and local environment of chromium ions. The intensity of the pre-edge peak associated with Cr6+ state increases with Mg-substitution, suggesting the formation of oxygen vacancies and charge transfer from chromium to oxygen. Cr L-edge analysis revealed a reduction in the core-hole lifetime and increased charge carrier mobility in Mg-substituted Cr2O3, contributing to enhanced electrical conductivity. Charge transfer multiplet (CTM) calculations confirmed that Cr3+ remains the dominant oxidation state. These calculations also highlighted the influence of splitting and hybridization on the electronic structure. Cr K-edge analysis further confirmed the dominant Cr3+ oxidation state and revealed the impact of Mg-substitution on the local coordination environment of Cr ions. Extended X-ray absorption fine structure (EXAFS) data analyzed using the Demeter package with FEFF6 integration demonstrated the retention of the corundum structure of Cr2O3 upon Mg-substitution, with minimal changes in the Cr-O bond lengths. The incorporation of Mg into Cr2O3 leads to an increase in the splitting (Delta o) of Cr 3d states. This increase in Delta o results in a blueshift of d-d transitions in the UV-Vis spectra. These findings indicate improved optoelectronic properties of Mg-substituted Cr2O3, paving the way for high-performance p-type transparent conducting materials.