Real disordered crystal structure and Curie temperature of intermetallic compounds Y2Fe17-xMx (M=Si or Al)

The crystal structure of intermetallic compounds Y2Fe17, Y2Fe15.3Al1.7 and Y2Fe15.3Si1.7 was studied by powder X-ray and neutron diffraction. The real disordered structure of the compounds was found to be a disordered variant of the Th2Ni17-type structure, in which the Y atoms from the 2b sites subs titute in part the Fe "dumbbells" on 4f sites and the Fe atoms occupy part of vacant 4e sites. Besides, the Y atoms implant in 2c sites in the iron pl ane of the compounds, which causes plane distortions and splitting of the 1 2j Fe sites into two subsites. The substitution of Fe by Si or Al was found to have a preferential character for sites in the order: 12k, 4f, 4e, 6g a nd 12j. Partial substitution of Al or Si for Fe is established as resulting in an increase in the atomic Fe-Fr spacing in the 4f "Jumbbell" site. The Curie temperature of the compounds Y2Fe17. Y2Fe15.3Al1.7 and Y2Fe15.3Si1.7 is proportional to the atomic Fe-Fe spacing in the "dumbbell" site. (C) 200 1 Elsevier Science B.V. All rights reserved.