Short-range-order diffuse scattering in decagonal Ni-rich Al-Ni-Co quasicrystals

An analytical expression of the diffuse scattering (DS) intensity due to short-range order derived in a recent paper [A. Yamamoto, Acta Crystallogr. Sect. A 66, 372 (2010)] is applied to analyze DS intensities of the S1 phase at 1120 K and the quenched basic Ni rich (b-Ni) phase in decagonal Al(70)Ni(22)Co(8) (d-Al(70)Ni(22)Co(8)) quasicrystals. The analysis is based on a microdomain model consisting of 20 angstrom clusters. The S1 and b-Ni phases are low-and high-temperature phases of d-Al(70)Ni(22)Co(8) so that microdomains with the S1 phase structure are assumed to be formed in the b-Ni phase and vice versa. The intercluster correlation of the 20 angstrom clusters within the microdomains is assumed to be the same as that in a corresponding completely ordered structure up to the third intercluster distance similar or equal to 32 angstrom. It is demonstrated that simulated DS intensity distributions reproduce characteristic features in the observed DS intensity in these phases. This suggests that the analysis of DS intensity is efficient for understanding phase transition mechanisms of quasicrystals. It also shows the effectiveness of the theory and applicability of cluster-based DS intensity calculations to real quasicrystals, which reduce the number of short-range-order parameters drastically.