Antiphase Domains in Ordered Au3Cu Alloys

Alloys having compositions from 42%−9% Cu in the Cu-Au system were investigated to determine the nature of the antiphase structures and the range of the ordered Au3Cu structure in this region. The single-crystal thin-film technique was used to prepare the specimens and the structure was determined by electron diffraction. The ordered Au3Cu I structure exists as an equilibrium phase from 38.5%−9% Cu. Unlike the Cu3Au and CuAu alloys, however, periodic antiphase structures are not observed as an equilibrium phase in these alloys. Increasing the electron-atom ratio by the addition of a third element, for example, Al, results in the formation of a periodic antiphase structures as predicted. It is shown that the low ordering temperature is responsible for the failure of a periodic antiphase structure to appear in these alloys.