We have studied the cubic to tetragonal phase transition in epitaxial SrTiO3 films under various biaxial strain conditions using synchrotron X-ray diffraction. Measuring the superlattice peak associated with TiO6 octahedra rotation in the low temperature tetragonal phase indicates the presence of a phase transition whose critical temperature is a strong function of strain, with TC as much as 50K above the corresponding bulk temperature. Surprisingly, the lattice constants evolve smoothly through the transition with no indication of a phase change. This signals an important change in the nature of the phase transition due to the epitaxy strain and substrate clamping effect. The internal degrees of freedom (TiO6 rotations) have become uncoupled from the overall lattice shape.
@article{arxiv.cond-mat/0303317,
title = {Anomalous Phase Transition in Strained SrTiO$_3$ Thin Films},
author = {Feizhou He and B. O. Wells and S. M. Shapiro and M. v. Zimmermann and A. Clark and X. X. Xi},
journal= {arXiv preprint arXiv:cond-mat/0303317},
year = {2007}
}