Temperature-dependent Raman scattering in PT and PMN-PT thin films

Raman spectroscopy was used to investigate PbTiO3 (PT) and 0.7Pb(Mg-1/3 Nb-2/3)O-3-0.3PbTiO(3) (PMN-PT) thin films prepared by the sol-gel technique and deposited on platinum-coated silicon, and Al2O3. The PT spectra reveal that the films are polycrystalline in nature and the frequencies of most of the modes are decreased as compared to those in single crystal or powder material. This result is due to grain under stress, which is caused by nonequilibrium defects. Temperature dependence (290-60 K) of the Raman half-width bands in PT/Al2O3 is discussed in terms of anharmonic processes involving three phonons, however, the main contribution to line broadening appears to be due to presence of defects. In the case of PMN-PT films the temperature dependence study indicates strong disorder in the system, predominantly, in the B sites of the ABO(3) perovskite structure. The bands are, therefore, interpreted as due to a breakdown in the phonon momentum conservation within the Brillouin zone. Micro-Raman measurements at different film positions indicate that PT/Al2O3, and PMN-PT/Pt/Si films are homogeneous, while PT/Pt/Si films show different microstructure in the middle and edge positions. Scanning electron microscopy, Fourier transform infrared spectroscopy, and x-ray diffraction techniques have been used for the structural characterization. (C) 1996 American Vacuum Society.