Tetragonal distortion and the domain structure of thin Pb(Zr,Ti)O₃/MgO(100) films

The paraelectric-cubic to ferroelectric-tetragonal phase transformation of thin Pb(Zr,Ti)O₃/MgO(100) films was studied in synchrotron X-ray scattering experiments. In the thin epitaxial films, the tetragonal distortion of the ferroelectric phase and the transition temperature were significantly reduced. In sharp contrast to the reported mixture of the a-type and the c-type domains in thicker films, the 250-Å-thick film was purely composed of the c-type domains in the tetragonal phase. We attribute the suppression of the transition to the substrate effect, which prefers the c-type domains near the interface, and reduces the tetragonal distortion to minimize the strain energy caused by the lattice mismatch.