A new polymorphic material? Structural degeneracy ofXing-Qiu Chen1, 2, W. Wolf3, R. Podloucky1, P. Rogl1 and M. Marsman4
1 Institut für Physikalische Chemie, Universität Wien - Liechtensteinstrasse 22A A-1090, Vienna, Austria
2 School of Materials and Metallurgy, Northeastern University Shenyang 110004, PRC
3 Materials Design s.a.r.l. - 44 av. F.-A. Bartholdi, F-7200 Le Mans, France
4 Institut für Materialphysik, Universität Wien - Sensengasse 8 A-1090, Vienna, Austria
(Received 26 March 2004; accepted in final form 21 June 2004)
Based on density-functional calculations, we propose that is a polymorphic material. We predict that at low temperatures the cubic , and the hexagonal and structures of the Laves phase compound are nearly equally stable within 0.3 or 30 . This degeneracy occurs when the atoms magnetize spontaneously in a ferromagnetic arrangement forming the states of lowest energy. From the temperature-dependent free energies at we predict a transition from the most stable to the structure, which is the experimentally observed structure at elevated temperatures.
61.50.Lt - Crystal binding; cohesive energy.
71.15.Nc - Total energy and cohesive energy calculations.
75.50.-y - Studies of specific magnetic materials.
© EDP Sciences 2004