Evolution of structural and optical-absorption properties in V xFe3−xO4

The evolution of structural and optical properties by V substitution in magnetite (Fe3O4) was investigated. V xFe3−xO4 (x≤1.0)(x≤1.0) compounds maintain a cubic structure of magnetite with V ions mainly having a valence of +3 and occupying octahedral sites, revealed by using X-ray diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. Optical constants of V xFe3−xO4 thin films measured by spectroscopic ellipsometry in the 1–8 eV range vary significantly with V composition. The octahedral Fe ions are interpreted as being responsible for the observed reduction in the strength of the major absorption structures of Fe3O4 by V doping. Thus, a number of charge-transfer transitions involving octahedral (egeg and t2gt2g) and tetrahedral (t2t2 and ee) Fe d states are identified as contributing to the optical absorption spectrum of Fe3O4 and their energy differences are estimated.