X-ray Study of Ternary Ordering of the Noble Metals in AgAuZn2 and CuAuZn2

Abstract

X‐ray measurements of the ternary long‐range order (LRO) of noble metals in AgAuZn₂ and CuAuZn₂ have been obtained using a high‐temperature diffraction camera. The behavior of the LRO parameter S as a function of temperature is similar to that in β brass; the order disappears gradually as the temperature is raised. However, S lies above that obtained for β brass when plotted as a function of T/T_c, T_c being the critical temperature for disordering. X‐ray Debye temperatures of 210°K for CuAuZn₂ and 200°K for AgAuZn₂ were obtained; these are in good agreement with expected values. The ratio T_c/T_m (T_m is the temperature of melting) was found to range from 0.56 to 0.58 in agreement with the correlation observed by Oriani. A simple distance dependence of the interaction energy between the noble‐metal atoms cannot be used to explain the observed T_c's. Data for T_c and T_m of AgAuCd₂ are also included.