Structural Instability during Cubic‐Tetragonal Transformation in Lead Titanate Single Crystals

Abstract

In this paper, we report the structural instability and premartensitic transformation phenomena in PbTiO3single crystals during tetragonal‐to‐cubic phase transformation and vice versa, studied using hot‐stage X‐ray diffraction and polarized optical microscopy. The present results suggest that theoretical predictions of a habit plane based upon phenomenological crystallographic theory and experimental values may vary over a certain range if the lattice perturbation due to crystal defects and structural instability during transformation are taken into consideration. In the course of the tetragonal‐to‐cubic phase transformation, X‐ray diffraction shows a broad peak, associated with an intermediate phase, up to several tens of degrees above Tc. Using heating‐stage optical microscopy, patches of bright bands and moiré fringes were often seen to form in advance prior to the arrival of a phase front during cubic‐to‐tetragonal transformation, especially when the specimens exhibited severe internal stress, indicating a generalized lattice perturbation during phase transformation.