Spectroscopic study of the electric field induced valence change of Fe-defect centers in SrTiO3

Abstract

The electrochemical changes induced by an electric field in Fe-doped SrTiO₃ have been investigated by X-ray absorption spectroscopy (XANES and EXAFS), electron paramagnetic resonance (EPR) and Raman spectroscopy. A detailed study of the Fe dopant in the regions around the anode and cathode reveals new insights into the local structure and valence state of Fe in SrTiO₃ single crystals. The ab initio full multiple-scattering XANES calculations give an evidence of the oxygen vacancy presence in the first coordination shell of iron. Differences in the length and disorder of the Fe–O bonds as extracted from EXAFS are correlated to the unequivocal identification of the defect type by complementary spectroscopical techniques to identify the valence state of the Fe-dopant and the presence of the Fe − V_Ö complexes. Through this combinatorial approach, novel structural information on Fe − V_Ö complexes is provided by X-ray absorption spectroscopy, and the relation of Fe–O bond length, doping level and oxidation state in SrTi_1−xFe_xO₃ is briefly discussed.