Electron diffraction analysis of plastically deformed icosahedral Al-Pd-Mn single quasicrystals

A technique is presented to determine quantitatively the phason strain fields in quasicrystals by electron diffraction analysis in a transmission electron microscope. The deviation vectors of diffraction spots from their ideal positions are measured and related to their physical and orthogonal reciprocal coordinates. Investigations have been performed on as-grown as well as plastically deformed Al-Pd-Mn single quasicrystals. It was found that the magnitudes of the shifts of the spots depend linearly on the length of the perpendicular-space component of the reciprocal coordinates, while such a correlation was not found for the respective physical-space component. This behaviour evolves more clearly with increasing plastic strain. The measured spot shifts were fitted according to a linear vector equation relating the shifts to the perpendicular reciprocal vectors. This provides the possibility of determining the entries of the first two rows of the so-called 'phason matrix'. It was found that the values of the matrix entries vary with position in a given sample and that they increase with increasing amount of plastic deformation.