Grain size effect on the phase transitions in oriented PbTiO3 thin films deposited by the sol-gel method on (111) Pt/Si

Oriented PbTiO3 thin films with different average grain sizes were prepared by the sol-gel method on (111) Pt/Si substrates. The phase transitions in the films were investigated by using high-temperature XRD measurements. It was found that the phase transition from tetragonal to cubic in the film of grain size similar to 210 nm occurs at about 480 degrees C, whereas it occurs at around 460 degrees C in the film of grain size similar to 130 nm. The transition is reversible but with about 20 degrees C hysteresis between cooling and heating. The Curie temperatures T-c measured for both films are lower than that of the bulk. The T-c decreases with grain size. Although an abrupt 90 degrees-domain absence occurs between the two films, no major change in the T-c was observed. In addition, it was observed that the change in the c-parameter with temperature is almost the same in both heating and cooling cycles whereas the a-value exhibits hysteresis. This results just the reverse of those reported previously. (C) 1998 Elsevier Science B.V.