Theoretical modeling of the complexes of iron impurities and oxygen vacancies in SrTiO₃

The combined use of ab initio quantum mechanical and x-ray absorption near edge structure (XANES) methods confirms that the oxygen vacancies (V_O) are located in the first coordination shell of Fe³⁺ ions in the cathodic region of electrocolored Fe³⁺-doped SrTiO₃. The binding energy of such a complex is estimated as ∼0.4 eV. The lattice distortions obtained in ab initio modeling and extended x-ray absorption fine structure experiments are in agreement. The predicted distortions make a minor effect on a simulated XANES signal, and its shape mainly depends on the presence of V_O in the Fe³⁺ first coordination shell. Additionally, formation of the Fe³⁺–V_O complex leads to disappearance of the phonon frequencies in the range of 620–760 cm⁻¹ of the calculated phonon spectrum.