Comparison of local order in icosahedral Al–Pd–Mn quasicrystal and in approximant phase by thermal neutron scattering

In a previous paper [R. Caudron, A. Finel, Y. Calvayrac, M. Fradkin, R. Bellissent, in: S. Takeuchi, T. Fujiwara (Eds.), Proceedings of the Sixth International Conference on Quasicrystals, Tokyo, May 26–30, 1997, World Scientific, Singapore, 1998, pp. 375–378], we presented the results of neutron diffuse scattering in an icosahedral Al–Pd–Mn single grain. The background intensity, measured away from any intense Bragg peak was in good agreement with a calculation based on the chemical disorder of the ξ′ approximant of the icosahedral phase whose structure has been resolved by Boudard et al. [M. Boudard, H. Klein, M. de Boissieu, M. Audier, H. Vincent, Philos. Mag. A 74 (1996) 939–956], by using X-ray diffraction. In order to check the generality of this diffuse background and to legitimate this interpretation of local order in quasicrystalline Al–Pd–Mn, we have now measured the diffuse scattering of the ξ′ phase itself and other icosahedral samples.