Monodomain strained ferroelectricPbTiO3thin films: Phase transition and critical thickness study

Abstract

This work demonstrates that instead of paraelectric ${\text{PbTiO}}_{3}$, completely $c$-oriented ferroelectric ${\text{PbTiO}}_{3}$ thin films were directly grown on $(001){\text{-SrTiO}}_{3}$ substrates by pulsed-laser deposition with thickness up to 340 nm at a temperature well above the Curie temperature of bulk ${\text{PbTiO}}_{3}$. The influence of laser-pulse frequency, substrate-surface termination on growth, and functional properties were studied using x-ray diffraction, transmission electron microscopy, and piezoresponse force microscopy. At low growth rates (frequency $l5\text{ }\text{Hz}$) the films were always monodomain. However, at higher growth rates (frequency $g8\text{ }\text{Hz}$) $a$ domains were formed for film thickness above 20--100 nm. Due to coherency strains the Curie temperature $({T}_{c})$ of the monodomain films was increased approximately by $350\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ with respect to the ${T}_{c}$ of bulk ${\text{PbTiO}}_{3}$ even for 280-nm-thick films. Nonetheless, up to now this type of growth mode has been considered unlikely to occur since the Matthews-Blakeslee (MB) model already predicts strain relaxation for films having a thickness of only $\ensuremath{\sim}10\text{ }\text{nm}$. However, the present work disputes the applicability of the MB model. It clarifies the physical reasons for the large increase in ${T}_{c}$ for thick films, and it is shown that the experimental results are in good agreement with the predictions based on the monodomain model of Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)].