Heung Chan

Using transmission electron microscopy, in-situ changes in ferroelastic domains in 0.7PbO 3 -0.3PbTiO 3 single crystals were observed at 60 to -163°C. At -163°C, the microscopic tweed morphology of the ferroelastic domains rotated by 90°, and certain orientation changes in the mesoscopic sawtooth domains took place. At this temperature, the ferroelastic domains became coarsened and certain S-shaped mesoscopic domains were reshaped. The disappearance and/or changes in the orientations of both the sawtooth and the ferroelastic domains were reversible upon return to room temperature. On heating to 60°C, both the mesoscopic sawtooth and the microscopic tweed domains were stable below 53°C. Above 53°C, the mesoscopic walls disappeared and the contrast of the tweed domains became blurred. Upon return to room temperature from 60°C, the mesoscopic domain patterns could not be retrieved, indicating that the transformation was irreversible. The morphology of the tweeds at this temperature indicated a structural transition from a two-variant domain state to a multivariant state, eliminating mesoscopic boundaries