Frey, Friedrich; Steurer, Walter
Disorder diffuse scattering from decagonal phase alloys.
In: Journal of Non-Crystalline Solids, Vol. 153-154, Nr. C: S. 600-605
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The isotypic decagonal phases Al70Ni15Co15 (ANC) and Al65Cu20Co15 (ACC) show remarkable diffuse scattering of various kinds and of different origins. Most prominent are ’modulated’ diffuse layers which are due to columns with doubled period along the unique ’periodic’ axis. There are long-range correlations along this direction, but only restricted correlations in the lateral, i.e. quasiperiodic arrangement of these columns. This ordering vanishes gradually upon heating to 800°C, but recovers fully after cooling down again. An explanation is given by a reversible chemical order/disorder process of the Ni/Co atoms which might be facilitated by diffusion within the columns. Diffuse scattering contributions within the Bragg layers are traced back to orientational disorder of the columns and to positional disorder as consequence of the ’longitudinal’ ordering process. In contrast to ANC and ACC, decagonal Al70.5Mn16.5Pd13 (AMP) reveals disorder phenomena only related to the quasiperiodic ordering. Disordering in decagonal phases seems to be partly specific for the thermodynamically stable state, and partly related to the growth conditions.