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(parallel to)\ below T-c. In addition, the weak dependence of the peak broadening with \G(perpendicular to)\ 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(parallel to)\ and \G(perpendicular to)\. 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.