Investigation of structural phase transition in polycrystalline SrTiO3 thin films by Raman spectroscopy

Polycrystalline SrTiO3 thin films were prepared by pulsed laser deposition technique. The phonon properties and structural phase transition were studied by Raman spectroscopy. The first-order Raman scattering, which is forbidden in SrTiO3 single crystal, has been observed in the films, due to the structural distortion caused by strain effect and oxygen vacancies. The Fano-type line shape of TO2 phonon reveals the existence of polar microregions in the STO thin films. The evolution of TO2 and TO3 phonons with temperature shows the occurrence of a structural phase transition at 120 K related to the formation of polar macroregions in the films.