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

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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/Tc, Tc 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 Tc/Tm (Tm 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 Tc's. Data for Tc and Tm of AgAuCd2 are also included.