Phonon mode behaviours of PbTiO3 thin films deposited on Pt/Si substrates

Phonon mode behaviours are investigated as a function of temperature from room temperature to 534 degrees C for PbTiO3 thin films deposited by the sol-gel method on Pt/Si substrates. Intense Raman scattering is observed at all temperatures. The spectra are analysed with a classical oscillator model to estimate the frequencies and damping factors of soft E(1TO) and A(1)(1TO) modes, and are compared with those of bulk single crystals. The spectrum consists of a remarkable central-mode-type scattering at all temperatures. All transverse optical modes are observed and proved to have a shift from their position in bulk single crystal. The soft E(1TO) and A1(1TO) modes do not appear to soften further on heating toward the ferroelectric-paraelectric transition. Their damping factors are larger, and do not diverge near the phase transition, in contrast to the findings of previous studies on bulk single crystal. The static dielectric constants along principal axes are calculated using the Lyddane-Sachs-Teller relationship as a function of temperature and are compared with those of the bulk single crystals. The Curie-Weiss constant derived from the temperature dependence of the dielectric constant along the c-axis has a value of 3.27 x 10(5) degrees C. The ferroelectric phase is expected to be stable up to a temperature as high as 577 degrees C for these films. A modified Devonshire thermodynamic theory is shown to be plausible for the explanation for the shifts in Curie temperature and dielectric constant for these films.