State analysis of fluorine-doped SnO2 (FTO) by 57Fe Mössbauer spectroscopy

Abstract

Fe doped FTO powders were prepared by a chemical precipitation method. Mossbauer spectra of FTO with several concentrations of Fe dopants were decomposed into two doublets (D1 and D2). A doublet with a small electric field gradient (D1) is assigned to Fe3+ in a small distorted site of the rutile structure, and another doublet (D2) to Fe3+ in a large distorted site due to F− ion and oxygen defect. Furthermore, with increase of the annealing temperature the isomer shifts tended to decrease. It suggests that Fe3+ bonds are more covalently bonded than ionic at the higher annealing temperatures. The surface layer of grains were also characterized by 57Fe CEMS. The defect structures of Fe doped FTO were estimated using the oxygen defect models of tin oxide [Mudarra Navarro et al., J. Phys. Chem. C, 119, 5596 (2015)].