Effect of cluster size on the chemical ordering in nanometer-sized Au-75at%Cu alloy clusters

The effect of cluster size on the chemical ordering in nanometer(nm)-sized Au-75at%Cu alloy clusters has been studied by means of transmission electron microscopy (TEM). It was found that the chemically disordered high-temperature phase, i.e. solid solution, becomes more stable than the ordered (L1(2)) low-temperature phase even at room temperature when the cluster diameter is reduced below approximately 5 nm. Simulation has revealed that when the lattice of these nm-sized Au-75at%Cu clusters is so soft that the Debye temperature of the clusters is depressed, the order-disorder transition temperature, T-c of nm-sized clusters falls below room temperature.