Characterization of oxygen vacancies in SrTiO3 by means of anelastic and Raman spectroscopy

Oxygen vacancies in reduced SrTiO3 are investigated by Raman spectroscopy and dynamic elastic modulus measurements. The anelastic spectrum is used to evaluate the amount and state of the O vacancies, which result to be almost completely paired and otherwise aggregated at a concentration of 0.5 mol. %, with only 1/6 of them isolated at room temperature. Raman spectra recorded as a function of temperature in as-grown and reduced samples are examined regarding the different processes which can contribute to them. Chemometric analysis is used to highlight the specific influence of oxygen vacancies on the Raman spectra. It is shown that oxygen vacancies induce a relaxation of selection rules leading to the activation of first-order lines even in the cubic phase. Furthermore, regions around oxygen vacancies are demonstrated to be responsible for the asymmetric broadening of Raman lines.