Study on the Ordered Phases with Long Period in the Gold-Zinc Alloy System I. Survey of Crystal Structures and Calorimetric Measurement

The crystal structures of the ordered phases in the Au-Zn alloy system have been studied in detail by means of X-ray and electron diffraction on single crystal samples, and the order-disorder and other kinds of phase transitions involved in the present system have also been studied by the measurement of specific heat. The previously proposed structures of Au_<3+>Zn, Au_3Zn [H], Au_3Zn [R] have substantially been confirmed and that of Au_5Zn_3 Only partly. Moreover, the details in these structures have been revealed : in Au_<3+>Zn some type of the strong lattice modulation is present, and in Au_3Zn [R] the two types of structure, Au_3Zn [R_1] and Au_3Zn [R_2] , certainly exist. The transition behavior of the alloys with changing temperature has been investigated on samples of various compositions and the thermodynamic data obtained are presented. The phase diagram of the Au-rich side of the present system is reasonably corrected by the present experiment. The orientation distribution of the ordered crystals formed in the originally disordered crystal and the nature of the transition, Au_3Zn [H]-Au_3Zn [R], are briefly discussed.