ON THE DETERMINATION OF THE BURGERS VECTOR OF QUASI-CRYSTAL DISLOCATIONS BY TRANSMISSION ELECTRON-MICROSCOPY

The contrast of dislocations in icosahedral quasicrystals observed by transmission electron microscopy is discussed in the framework of the kinematical theory of electron diffraction. It is found that, owing to the special structural features of dislocations in quasiperiodic lattices, there are two basically different imaging conditions for which the contrast can vanish. The conditions are established for contrast experiments in which the direction of the Burgers vector components can be determined in physical and orthogonal space. Provided that the dislocation displacement field fulfils certain requirements, contrast experiments employing both extinction conditions permit the defect to be characterized by the direction of a Burgers vector in the six-dimensional reference space of icosahedral quasicrystals.