A PbTiO3 thin film prepared on silicon substrate by sol-gel technique has been studied by micro-Raman spectroscopy and x-ray diffraction (XRD). The spectra, in comparison to the single crystal work, show high background in the low frequency region and Raman lines are broader, thus revealing the polycrystalline nature of the film. The frequencies of the Raman bands in the film are clearly shifted to lower frequencies compared to the corresponding ones in the single crystal or powder forms. This phenomenon is similar to the hydrostatic pressure effect on the Raman lines of PbTiO3 single crystal. The film, therefore, has grains under stress. This stress is caused by nonequilibrium defects and diffusion at the interface. Measurements at different film positions showed variations in the frequency and width of the Raman bands which are associated with the stress and grain size inhomogeneities. The measured shift in the Raman frequencies suggests grain sizes ≤1 μm. XRD indicates grain size of around 22 nm and an average stress around 1.3 GPa, which was determined using the measured shift for the c-lattice constant.

Oxygenated CdTe films prepared by r.f. sputtering have been shown to have band gap energies between 1.48 and 3.35 eV, depending on the amount of oxygen incorporated in the CdTe matrix. Samples with oxygen concentrations above 7 at.% are amorphous, whereas those with oxygen concentrations below 7 at.% are polycrystalline, as determined by x-ray and Raman measurements. The Raman spectra of the polycrystalline samples show that there is ca. 4 at.% Te in the form of inclusions under high pressure, which is relatively easy to detect owing to the enhanced Raman cross-section of Te. The Raman spectra of the amorphous samples is dominated by a single broad band at 159 cm-'. The fact that tellurates in general show a similar band, in spite of their different vibrational density of states, indicates that it corresponds to Te-Te bonds in the amorphous matrix.

Raman spectra of SrBi2Ta209 (SBT), Bi3TiNh09(BTN), and x(SBT) + (1-x)(BTN) samples were studied for the first time in the low frequency region. The BTN spectra show two features around 33 and 41 cm-', while only one feature, around 30 cm-', is found in SBT. The stoichiometric evolution of the Raman spectra shows that the frequency positions of these bands decrease as x changes from 0 to 1. Strong correlation is found between the frequency positions of these modes and both the Curie temperature and the a-parameter. The results are interpreted in terms of the ferroelectric displacive modes, which are responsible for the strong spontaneous polarization along a-axis. The band around 65 cm-'is assigned to oxygen motion in the B202 layer.

A PbTiO3 thin film prepared on silicon substrate by sol-gel technique has been studied by micro-Raman spectroscopy. The spectra, in comparison to the single crystal work, show high background in the low frequency region and Raman lines are broader, thus revealing the polycrystalline nature of the film. The frequencies of the Raman bands in the film are clearly shifted to lower frequencies compared to the corresponding ones in the single crystal or powder forms. This phenomenon is similar to the hydrostatic pressure effect on the Raman lines of PbTiO3 single crystal. The film, therefore, has grains under stress. This stress is caused by non-equilibrium defects and diffusion at the interface. Measurements at different film positions showed variation in the frequency and width of the Raman bands which are associated with the stress and grain size inhomogeneities. The measured shift in the Raman frequencies suggest grain sizes ≤l μm. XRD indicates grain size around 22 nm.

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