Phase stability and transformation in nanometre-sized Au[sbnd]Pb alloy clusters produced by spontaneous alloying

Abstract

The structure and phase transformation in nanometre (nm)-sized Au-Pb alloy clusters have been studied in situ by means of transmission electron microscopy, in order to see the difference in phase equilibrium between a bulk material and the corresponding nm-sized cluster. When lead (or gold) atoms are vapour-deposited on to nm-sized gold (or lead) clusters kept at ambient temperature, spontaneous dissolution of the solute atoms into the clusters takes place and homogeneous Au-Pb alloy clusters are formed. The solid solubilities of lead and of gold for the Au-Pb solid solution clusters are increased markedly as compared with those for the corresponding bulk materials. A stable intermetallic compound formed preferentially in Pb-enriched Pb-Au alloy clusters is AuPb₂, for which a heat of formation is negative. The phase transformation from Au-supersaturated Pb-Au solid solution clusters to single crystalline AuPb, clusters takes place during a short period, and is similar to a ‘martensitic’ transformation.