Structure dynamics of strongly reduced epitaxial BaTiO3-x studied by Raman scattering

Raman scattering technique was used to study structure dynamics of strongly reduced epitaxial barium titanate (BaTiO3-x) thin films grown on MgO (1 0 0) substrates by laser molecular beam epitaxy under different oxygen pressures from 10(-2) to 10(-5) Pa. X-ray diffraction and asymmetric rocking curves indicate that lattice parameters c and c/a ratio increase, and a slightly decreases with decreasing oxygen pressure, indicating increased lattice volume of BaTiO3-x thin film. Raman spectra confirm that BaTiO3-x thin films are in tetragonal phase with some deviated features, which maybe origin from tensile strain at film-substrate interface due to lattice parameter mismatch. Moreover, two weak peaks in Raman spectra of BaTiO2.52 thin film grown under 3.0 x 10(-5) Pa may be induced by second-order two-phonon processes. Raman peaks shift towards lower frequencies with decreasing oxygen pressure during deposition, suggesting a decrease of the stress in BaTiO3-x thin films. In the meantime, Raman peaks become broadened, which may be attributed to higher degree of structural disorder in strongly reduced BaTiO3-x lattice structure. (c) 2005 Elsevier Ltd. All rights reserved.