SYNCHROTRON X-RAY STUDIES OF DIFFUSE-SCATTERING IN AN AL-CU-CO 2-DIMENSIONAL DECAGONAL QUASI-CRYSTAL

Diffuse scattering along the (10000) direction in the quasiperiodic plane in a single-phase decagonal Al-Cu-Co quasicrystal has been studied by the synchrotron X-ray diffraction technique at room temperature. The line shapes along both longitudinal (L) and transverse (T) directions were measured. A peculiar anisotropic line shape along the L direction was found. Two-dimensional contour maps reveal that some peaks have strong diffuse scattering components and that they are elongated along the T direction. The observed diffuse scattering profile varies from peak to peak, although all the peak positions are aligned in the same direction in reciprocal space. The diffuse scattering component, which is elongated along the T direction, can be fitted by a single Lorenzian with a linewidth about 20 times broader than that of the Bragg peak. No simple G(parallel-to) or G(perpendicular-to) dependences for the diffuse scattering intensity were observed, in disagreement with the current status of the theories. The origin of discrepancies between experiment and theory is suggested.