A study was made of the structures of twin boundaries, and of the interfaces of orthogonally orientated twins, by using high-resolution electron microscopy and electron diffraction techniques. It was found that twins were the predominant defects when the deviation from O stoichiometry was less than 0.5. At temperatures below about 750C, the oxide underwent a tetragonal-to-orthorhombic structural phase transition. This resulted in twinning on {110} planes. The twins formed in order to reduce the strain energy that was due to the change in shape and volume which resulted from the phase transformation. The spacing of the twin lamellae was determined by minimizing the total energy that was associated with the strain energy (at the grain boundaries where the twins terminated), as well as the interfacial energy of the twin boundary.

Y.Zhu: Materials Science Forum, 1996, 207-209, 381-4