Long Period Superlattice Cu3Au II

A detailed study of the Cu-Au system between 25–50 at. % Au was made to determine the range of stability of the long period superlattices found in this system. The single-crystal thin film technique was used to make the samples, and the structure was determined using electron diffraction. It was found that a one-dimensional long period superlattice exists as an equilibrium phase from about 30% Au, substantiating Scott's original observation, to 60% Au. From about 30% to 38% Au, the antiphase structure is the Cu3Au II type, while at higher Au content, the structure is the CuAu II type. The domain size M was found to decrease continuously from a value of about 10 at 30% Au to 5 at 50% Au, regardless of the change in structure when crossing the phase region between Cu3Au and CuAu. Small amounts of Al added to a sample having the CuAu II structure and an Au content of 40%, decreased the domain size in a manner identical to that observed for stoichiometric CuAu II. The addition of Al to a sample having an Au c...