On the stability of chemical order in small ordered-alloy particles

Abstract

The reduction in the chemical order of small particles of long-range ordered alloys has recently been discussed by Fukami and Tanaka (Phil. Mag. Lett. 84 33 (2004)) in the framework of the Bragg–Williams model, in apparent accordance with experiment. We re-examine the discussion in the same framework with a closer inspection of the quantitative details. While it reproduces fairly well the lowering of the order–disorder transition temperature of Cu₃Au particles of about 10 nm in size, the model is unable to explain the extended stability of the disordered state observed for smaller particles at room temperature; the order–disorder transition temperature does not fall below half of the transition temperature of bulk materials.

Acknowledgements

We thank Professor T. Tadaki for calling our attention to the relevant literature, and Ms N. Suga for discussions.