Study of the Long-Period Ordered Alloy Cu3Pt

The existence range of the one-dimensional long-period ordered alloy Cu 3 Pt (L1 2- s ) on the equilibrium diagram has been determined by X-ray diffraction, single crystal specimens having been prepared and quenched at various temperatures. As the result it has become clear that there occurs a two-step transition L1 2 →L1 2- s →A1 by heating-up in this alloy system, and this transition has been confirmed by specific heat measurements. The half long-period M of L1 2- s phase has been measured from separations of split superlattice reflections. M increases with decreasing platinum content, and the behavior of this concentration dependence is well explained by the relation between M and e / a based on Sato-Toth's idea. M decreases as the temperature approaches T c , in the same way as in Cu 3 AuII but contrary to the behavior in Ag 3 Mg. Some argument is given on the temperature dependence of M and the degree of order in the long-period lattice of Cu 3 Pt.