Structural defects which were observed, by means of transmission electron microscopy, in approximant phases were identified as being phason defects. By making assumptions concerning their motion under an applied shear strain, it was shown that 2 approximant phases could be related by a phase transformation which occurred via plastic deformation. Other experimentally observed approximant phases could be interpreted as being intermediate states of such a phase transformation. The atomic motions which corresponded to these phason shifts were examined on the basis of high-resolution electron microscopic observations and crystallographic data which had been obtained from a single-crystal X-ray study of one of these approximants. A description of this transformation in 6-dimensional hyperspace was proposed in order to establish a relationship with the icosahedral quasi-crystalline state. The possibility that plastic deformation of the icosahedral phase, which occurred without any strain-hardening effect, could result only in the motion of phason defects was considered.

H.Klein, M.Audier, M.Boudard, M.De Boissieu, L.Beraha, M.Duneau: Philosophical Magazine A, 1996, 73[2], 309-31