Structure of Al-(Li,Mg)-Cu icosahedral alloys studied by pulsed neutron scattering

Abstract

We present results from a pulsed neutron study of ${\mathrm{Al}}_{55}$ ${\mathrm{Cu}}_{10}$ ${\mathrm{Li}}_{35\mathrm{-}\mathrm{x}}$ ${\mathrm{Mg}}_{\mathrm{x}}$(x=0 and 5) and ${\mathrm{Al}}_{51}$ ${\mathrm{Cu}}_{12.5}$ ${\mathrm{Mg}}_{36.5\mathrm{-}\mathrm{x}}$ ${\mathrm{Li}}_{\mathrm{x}}$ (x=0 and 23.5) icosahedral alloys. Structure factors and pair distribution functions of these alloys are obtained from single-phase samples. Contrast variation of diffraction patterns, due to substitution of Li atoms by Mg atoms, is observed. Our results indicate that Al-Cu-Li and Al-Cu-Mg i phases are isostructural, but Al-Cu-Li i phase, which is more stable than Al-Cu-Mg i phase, has better medium- and long-range order. Our studies support the (Al,Zn${)}_{49}$ ${\mathrm{Mg}}_{32}$-type icosahedral structure of these alloys proposed by Henley and Elser.