PROMINENT FERROELASTIC DOMAIN-WALLS IN BIVO4 CRYSTAL

The domain structure of ferroelastic BiVO4 crystals was investigated by x-ray diffraction, nuclear magnetic resonance, optical polarizing microscopy, transmission electron microscope, and electron diffraction techniques. From these results, it is found that the BiVO4 crystals have only prominent W walls and no non-prominent W' domain walls. A model of the twin structure is suggested, and all experimental results are explained in terms of this model. However, the prominent W wall obtained from our experimental results should not occur in the ferroelastic species 4/mF2/m previously reported. From the acoustic symmetry character of the elastic behaviour, it has been established that there exist two possible W and W' walls for permissible planar walls that are consistent with all experimental observations. Thus, it can be concluded that the BiVO4 crystals having only the W walls found by our group and W' walls obtained by other groups are consistent with the ferroelastic species 4/mmmF2/m rather than 4/mF2/m.