Stress effect and evidence of ferroelectric weakening in highly c-axis-oriented PbTiO3 thin films

3 were successfully grown on Pt-coated SrTiO₃ single-crystal substrates by metalorganic chemical vapor deposition (MOCVD) and were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The as-deposited thin films were found to be highly (001)-oriented with an average grain size of about 0.3 μm. Both a decrease of the tetragonality and a frequency downshift of the long-wavelength optical phonons were observed and attributed to the effect of compressive stress in the thin films. However, Raman scattering studies estimated a stress value of 2.6 GPa, which is much larger than the value of 0.75 GPa obtained from the XRD analyses. Raman spectroscopic studies also confirmed the grain-size-related disorder feature in the as-grown PbTiO₃ thin films. Structural investigations implied the weakening of ferroelectricity in the heteroepitaxial ferroelectric thin films. Received: 1 April 1997/Accepted: 14 July 1997