Twin structure deduced from elastic constants of ferroelastic BiVO4

The domain walls of ferroelastic BiVO 4 crystal recently investigated by the nuclear magnetic resonance and X-ray diffraction methods were found to be different from those reported by others. The concept of ferroelasticity is considered in terms of the properties of the elastic constants of materials that undergo ferroelastic phase transitions. The acoustic symmetry character of the elastic behaviour of the tetragonal scheelite structure is shown to be exactly the same as that of the point groups 4/m and 4/mmm. From these results domain walls are derived: (1p0) planes with p=0.724 and p=1. The theoretically deduced angles are consistent with an observed value of 37.4 degrees and another value of 44.5 degrees . The authors have established that there exist two possible orientations for permissible planar walls that are consistent with experimental observations.