PNNL

Abstract

We provide a detailed theoretical analysis of the character of optical transitions and band gap reduction in (Fe1-xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Optical absorption bands for x = 0.0, 0.5, and 1.0 are assigned on the basis of timedependent density functional theory (TDDFT) calculations. A band-gap reduction of as much as 0.7 eV with respect to that of pure a-Fe2O3 is found. This result can be attributed to predominantly two effects: (i) the higher valence band edge for x ˜ 0.5, as compared to those in pure a-Fe2O3 and a-Cr2O3, and, (ii) the appearance of Cr ? Fe d–d transitions in the solid solutions. Broadening of the valence band due to hybridization of the O 2p states with Fe and Cr 3d states also contributes to band gap reduction.