New Complex Phase in the Copper-Gold System

Abstract

At the composition 31.6 at. % gold, the equilibrium diagram shows a two-phase mixture of ordered and disordered material extending from 320°C to 350°C. However, a long anneal in this interval results in an x-ray pattern showing superstructure reflections with strong satellites. The satellite pattern is obtained both by lowering and raising the temperature, and hence is believed to represent an equilibrium structure. The satellite pattern is interpreted in terms of a Cu3Au II type structure, which is derived from the ordered Cu3Au I by introducing antiphase domain displacements (a2+a3)/2 at regular intervals along the a1 axis, exactly analogous to the development of CuAu II from CuAu I. At 31.6 at. % gold, the period is 18a1 (9 a1 between consecutive domain boundaries). Between 320°C and 335°C, there is a two-phase mixture of Cu3Au I and Cu3Au II. From 335°C to about 345°C the structure is that of Cu3Au II. From about 345°C to 350°C there is probably a two-phase mixture of Cu3Au II and disordered material, but this has not been established. The satellite pattern is also obtained at the composition 29.2 at. % gold, and it is likely that the Cu3Au II type structure exists over a range of compositions on the gold rich side of Cu3Au.

On the stability of periodically antiphased alloys

“…was well established when lowering temperature at constant cornposition. But according to this theory, AuCLLII would be an exception, which opinion is still alive 141. that time, Pianelli [ S ] arid Scott[6] had already shown the existence of AuCu, I1 (PAP) in an intermediate range of temperature, with the same thermal + izucu, Ir (PAP) + A~c~, I (1~1,) , with decreasing temperature.More recently, two new instances of transition "disorder + PAP ---f order" have been reported,Gratias et al (1972) [ 7 ] for Au,Cu and Ogawa et al(1973) …”

Au Alloy Formation with Sn–Pb or Sn–Zn Solder Nanoparticles

“…Differences of the periodic fringe distance in a particle suggests that deviation of atomic ratio from Au 3 Zn composition took place during the ordered alloy formation upon the deposition of Au. [18][19][20][21] Even if the SnPb-Au or SnZn-Au evaporation sequences were altered to Au-SnPb or Au-SnZn, with the same evaporation amount of metals, the same alloy formation was observed. The same result was also noted in the binary Au-Pb system.…”

Some aspects of short-range order

“…There is, however, evidence that the ordering pattern is différent in thin filmes than in the bulk. Scott [18] observed a différent diffuse scattering at the surface of a single crystal of Cu3Au than in the interior. (This difference, however, could also be due to differences in composition at the surface as a result of etching prior to the ordering treatment.)…”