Structure of Al-Mn-Cr-Si quasicrystals studied by pulsed neutron scattering

Abstract

The atomic structure of rapidly quenched quasicrystals, ${\mathrm{Al}}_{80}$${\mathrm{Mn}}_{20}$, ${\mathrm{Al}}_{75}$${\mathrm{Mn}}_{20}$${\mathrm{Si}}_{5}$, and ${\mathrm{Al}}_{75}$${\mathrm{Mn}}_{15}$${\mathrm{Cr}}_{5}$${\mathrm{Si}}_{5}$, was studied by pulsed neutron scattering. The pair distribution function was obtained by a direct Fourier transformation of the structure factor, and by assuming isomorphous substitution of Cr for Mn the differential distribution function (DDF) was determined. The addition of Si was found to increase the medium-range order significantly. The DDF from Mn atoms indicates the presence of a quasicrystalline substructure which is occupied both by Mn and Al atoms. The atomic structure of these solids, therefore, is significantly different from that of quasicrystalline ${\mathrm{Pd}}_{58.8}$${\mathrm{U}}_{20.6}$${\mathrm{Si}}_{20.6}$.