A. Teresiak et al., FORMATION OF MODIFIED TBCU7 AND TH2ZN17 TYPE STRUCTURES DURING ANNEALING OF MECHANICAL-ALLOYED SM-FE POWDERS, Journal of alloys and compounds, 274(1-2), 1998, pp. 284-293
Compounds with the nominal composition near Sm2Fe17 were prepared by m
echanical alloying starting from the elemental powders and subsequent
annealing at temperatures, T-A, between 600 degrees C and 900 degrees
C. For crystal structure investigations of the non-equilibrium phases
formed at various temperatures, XRD methods with following Rietveld an
alysis were applied. For T-A between 600 degrees C and 750 degrees C a
modified TbCu7-type structure of space group P6/mmm was found, in whi
ch the Fe(2c) site is replaced by the partially (1/3) and randomly occ
upied Fe(6l) site. Its approximate composition is SmFe8.8-9.0. For T-A
between 800 degrees C to 900 degrees C a disordered modified Th2Zn17
structure (space group R (3) over bar m) was found that is formed by i
ntroducing additional randomly occupied Fe (6c) and Sm(3a) positions,
respectively. The degree of order of Sm atoms and Fe-dumbbells along t
he c-direction increases with increasing T-A. A decrease in the Fe con
centration in the cell is observed for increasing T-A. The completely
ordered stoichiometric Th2Zn17-type structure could not be reached by
annealing samples prepared from the ball-milled elemental powders. (C)
1998 Elsevier Science S.A.