UNUSUAL STRUCTURAL MODIFICATION IN THE TI68FE26NI1SI5 QUASI-CRYSTALLINE PHASE

We report here the formation of a class of materials in the rapidly so lidified Ti68Fe26Ni1Si5 system based on transmission electron microsco pic exploration of the electropolished melt-spun ribbons. The phase re ported here pertains to a modification of the icosahedral phase leadin g to tetrahedral symmetry with no discernible periodicities, unlike th ose of earlier known rational approximant phases. The analysis of the selected area diffraction patterns of these phases revealed variable l inear phason strains in the shifted spots of undistorted twofold recip rocal rows. The experimentally observed reciprocal vectors in these di rections have been suggested to arise owing to their dependence on bot h the physical and pseudospace components vis-re-vis that of the icosa hedral phase. It has been argued that such a dependence may arise owin g to the presence of the nonlinear motif having components in both the spaces in the higher-dimensional structural description.