Jahn-Teller distortion around Fe~(4+) in Sr(Fe_xTi_(1-x))O_(3-δ) from x-ray absorption spectroscopy, x-ray diffraction, and vibrational spectroscopy

摘要

Sr(Fe_xTi_(1-x))O_(3-δ) perovskites (strontium titanate ferrite solid solution) with well-defined oxygen stoichiom-etry have been studied as a function of iron concentration by x-ray diffraction, Fe and Ti K-edge x-ray absorption spectroscopy (XAS), and vibrational (Raman and infrared) spectroscopy. In reduced Sr(Fe_xTi_(1-x))O_(3-x/2) samples, the analysis of the Fe K-edge extended x-ray absorption fine structure indicates the expected presence of oxygen vacancies V_0 in the first coordination shell of Fe~(3+) ions. In oxidized Sr(Fe_xTi_(1-x))O_3 samples, the combination of XAS and vibrational spectroscopy results yields strong indications for the presence of a Jahn-Teller distortion around Fe~(4+) ions, which is most pronounced for x ≈ 0.03 and decreases for higher iron concentrations.