Anomalous phase transition in strained SrTiO3 thin films

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 T-C as much as 50 K 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 epitaxial strain and substrate clamping effect. The internal degrees of freedom (TiO6 rotations) evolve independently from the overall lattice shape. (C) 2003 American Institute of Physics.