Ordering and correlation of cluster orientations in CaCd₆

Abstract

In order to study the low-temperature phase transition in CaCd₆, which is attributed to a reordering of the innermost tetrahedral cluster shells, accurate Embedded-Atom-Method potentials are developed for this system. With these potentials, the ideal cluster structure and the couplings between neighbouring clusters are determined. From these data, an effective Hamiltonian for the cluster orientations is derived. The Hamiltonian is used in Monte Carlo simulations, which exhibit a sharp jump in the internal energy near the expected transition temperature.

Acknowledgements

This work was supported by the European Network of Excellence ‘Complex Metallic Alloys’ (CMA) and by the German Research Council (DFG) within the Collaborative Research centre 382. MM also acknowledges support by Grant Agencies for Science of Slovakia, grant nos. VEGA 2/5096/25 and APVT-51052702.