Microraman Study of PbTiO₃ Thin Film Prepared by Sol-Gel Technique

Abstract

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.

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

“…6 The temperature dependence of the halfwidth ⌫ of the phonon can be expressed as The primary possible mechanism in a perfect crystal is decay of the optical phonon into two acoustic phonons with opposite wave vectors of equal magnitude.…”

“…1 PbTiO 3 ͑PT͒ is one such ferroelectric material, having a high spontaneous polarization and a high pyroelectric coefficient. 3,6 However, apart of the stress contribution produced for the difference in thermal expansion between PbTiO 3 and the substrate, the origin of the stress has been explained invoking nonequilibrium defects. 2 In particular, combining these perovskite oxides in thin film form with semiconductor technology results in the wide variety of applications mentioned above.…”