Electron microscopy of dislocations in quasicrystals

Abstract

The Bragg diffraction contrast of dislocations in icosahedral Al₆₂Cu_25.5Fe_12.5 was investigated experimentally in the transmission electron microscope. In good agreement with the results of a theoretical treatment based on the kinematical column approximation, it was found that the contrast vanishes under two basically different diffraction conditions. This is different from the behaviour in normal crystals and is due to the special structural features of dislocations in quasiperiodic lattices. Quantitative evaluation of the results indicates that the phason component of the dislocation strain field is substantially stronger than the phonon component.