Structure Relations and XRD Patterns of the Disorder-Order Transition of Metastable RE{sub}2TM{sub}17 Alloys

摘要

By using non-equilibrium methods and subsequent annealing, rare-earth transition-metal-alloys with the nominal chemical composition 2:17 show a hexagonal metastahle TbCu{sub}7 like structure. This disordered hexagonal (P6/mmm) metastable compound can be represented by a rhombohedral cell by using a coll transition of the hexagonal space group P6/mmm into the translationsgleiche subgroup P 31 w (162) and subsequently into the klassengleiche subgroup II b R 3m. The atomic positions of the obtained rhombohedral cell correspond to appropriate coordinates in the hexagonal cell. In that way, a partial order of the 2:17 structure can be described. For the binary system Sm-Fe, a compound with similar structure and the formula SmFe{sub}8.5 exists. Examples are given for the obtained phases after ball milling the elemental powders Fe and Sm and subsequent annealing, and also after HDDR of Sm{sub}2Fe{sub}17.