TRANSIÇÕES ELETRÔNICAS EM α-Fe₂O₃: MODELOS TEÓRICOS E LIMITAÇÕES

ELECTRONIC TRANSITIONS IN α-FE₂O₃: THEORETICAL MODELS AND LIMITATIONS

ELECTRONIC TRANSITIONS IN α-FE₂O₃: THEORETICAL MODELS AND LIMITATIONS. Addressing electronic transitions of hematite (α-Fe₂O₃) is still considered a topic in active debate, even though it is one of the most widely used compounds from ancient times to the present and also one of the most extensively investigated iron oxides. In this review, a general analysis of the approaches and theoretical models which had been used to explain the electronic absorption spectrum of α-Fe₂O₃, from the frst proposal presented by Tandon and Gupta (1970) to the more recent results obtained by quantum mechanical calculations, is presented. The analysis of the already published studies is made pointing out the main factors that must be considered to allow a more reliable understanding of the UV-Vis-NIR spectra of α-Fe₂O₃. Furthermore, controversies in the calculated results are discussed, analysing the suitability of each of the approaches used. Reasons for differences observed in the experimental data reported in the literature are also discussed.

Keywords:
hematite; electronic absorption spectrum; band assignment