Diffuse scattering from an Al₇₂Ni₂₀Co₈ decagonal quasicrystal on an order–disorder transformation

Non-uniform distortion induced by superstructure domains has been observed during the ordering process of an order–disorder transformation in a single decagonal quasicrystal of Al₇₂Ni₂₀Co₈. The full width at half maximum (FWHM) of the fundamental reflections increased below the transformation temperature, T_c. At the same time, the integrated intensity of the fundamental reflections varied drastically at T_c. A small hysteresis was also observed in the temperature dependences of both the FWHM and the integrated intensity of the fundamental reflections. Peak broadening of the fundamental reflections is predominantly dependent on |G^∥ | below T_c. In addition, the weak dependence of the peak broadening with |G^⊥ | is extracted from the observed FWHM of the fundamental reflections. After deconvolution, the FWHM of the fundamental reflections appears to be a linear combination of |G^∥ | and |G^⊥ |. Coexistence of the non-uniform distortion and of the random phason strain contributes to the ordering process below T_c. The diffuse scattering from atomic short-range order (SRO) was distributed around the ideal positions of the superstructure reflections. The SRO diffuse scattering disappeared completely above T_c + 10 K. In addition, a small hysteresis of the SRO diffuse scattering was found in the temperature cycle.