This work demonstrates that instead of paraelectric ${\text{PbTiO}}_3$, completely $c$-oriented ferroelectric ${\text{PbTiO}}_3$ thin films were directly grown on $\left(001\right){\text{-SrTiO}}_3$ 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 $<5\text{Hz}$) the films were always monodomain. However, at higher growth rates (frequency $>8\text{Hz}$) $a$ domains were formed for film thickness above 20–100 nm. Due to coherency strains the Curie temperature $\left(T_c\right)$ of the monodomain films was increased approximately by $350°\text{C}$ 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 $\sim 10\text{nm}$. 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)].

• Received 10 July 2008

DOI:https://doi.org/10.1103/PhysRevB.78.104112