On the Superstructure of the Ordered Alloy Cu3Pd II. X-ray Diffraction Study

The structures of the ordered copper-palladium alloys in the composition range from 15.5 to 28.5 atomic per cent Pd were investigated by X-ray diffraction, using both single crystals and power specimens. The alloys with the composition of 20.8 to 25.8 atomic per cent Pd have an anti-phase domain structure in a fully ordered state cooled slowly from 450°C to room temperature in four months. This structure is formed from the elementary face-centered tetragonal lattice, in which the atoms arrange themselves as in the ordered alloy Cu 3 Au but step-shifts occur at a definite period along the tetragonal axis. On the other hand, the alloys of 27.3 and 28.5 atomic per cent Pd were confirmed to possess a more complicated anti-phase domain structure characterized by the two kinds of out-of-step, which was already elucidated by the electron diffraction study in Part I. Variation of both the lattice parameters and the periods of anti-phase domain with composition were also studied.