Raman Study of Oxygen Reduced and Re-Oxidized Strontium Titanate

We report Raman study of oxygen reduced single crystal strontium titanate. Oxygen reduction leads to the appearance of the forbidden first-order Raman peaks, as well as spectral features attributed to the local vibrational modes associated with oxygen vacancies. This assignment is supported by ab initio calculations of phonon modes in SrTi O3 with introduced oxygen vacancies. Raman studies of re-oxidized samples show the same spectra as the initial single crystals. Comparison of Raman spectra of SrTi O3 thin films and reduced SrTi O3 single crystals demonstrates the importance of other factors such as polar grain boundaries in the lattice dynamical behavior of thin films.