Formation of AB 2 -intermetallics by diffusion in the Au–Sb–Bi system

Abstract

Binary diffusion couples, in which one single-phased product layer is growing between pure elements, were employed to study the diffusion properties of Au2Bi- and AuSb2-intermetallics at 230 and 330 °C. The position of the Kirkendall-marker plane inside the reaction zones revealed that in this temperature range the minority element is the faster diffuser in the Laves-phase Au2Bi as well as in AuSb2. The concept of integrated diffusion coefficient is used to describe the growth kinetics of the intermetallic compounds. The integrated diffusion coefficient in an intermetallic is related to the tracer diffusivities of the components and the thermodynamic stability of the phases involved in the interaction. The tracer diffusion coefficients were deduced from the interdiffusion experiments. The isothermal cross-section through the ternary phase diagram Au–Sb–Bi at 230 °C was constructed by means of the diffusion couple technique. No ternary phases are found in this system. Both intermetallic compounds Au2Bi and AuSb2 are in equilibrium with the (Sb,Bi)-solid solution. The solubility of Sb in the Laves-phase Au2Bi was found to be negligible. Up to about 10.5 at.% of Bi can be dissolved in the AuSb2-phase, the Bi-atoms substituting Sb in the cubic lattice of AuSb2.