Study of the Long-Period Ordered Alloy Cu₃Pt

Abstract

The existence range of the one-dimensional long-period ordered alloy Cu₃Pt (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 L1₂→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 Cu₃AuII but contrary to the behavior in Ag₃Mg. Some argument is given on the temperature dependence of M and the degree of order in the long-period lattice of Cu₃Pt.