Crystal structure of Sm2Fe17-yMy compounds with M=Al, Si, Ga

The lattice parameters and atomic positions of the atoms, in particular the M-atoms, for arc-melted Sm2Fe17-yMy compounds with M=Ga, Al, Si and y=0, 1 , 2 were determined using X-ray diffraction methods and subsequent Rietveld refinement. An increasing unit cell volume was found for M=Ga and Al, and a decreasing cell volume for substituting Fe by Si. Ga occupies the atomic position 18h in the rhombohedral R-3m Zn2Th17-type structure in all cases, whereas Al and Si occupy the 18h position up to a concentration of 1 atom p er formula unit and for a larger concentration; additionally, the 18f posit ion. Despite of the different behaviour of the lattice constants, the neare st neighbour distances were found to behave similarly for all substituting elements in Sm(2)Fe(17-y)My because of different shifts of the atomic sites . (C) 2001 Elsevier Science B.V. All rights reserved.