Formation of modified TbCu 7 and Th 2Zn 17 type structures during annealing of mechanical-alloyed Sm–Fe powders

Abstract

Compounds with the nominal composition near Sm 2Fe 17 were prepared by mechanical alloying starting from the elemental powders and subsequent annealing at temperatures, T A, between 600°C and 900°C. For crystal structure investigations of the non-equilibrium phases formed at various temperatures, XRD methods with following Rietveld analysis were applied. For T A between 600°C and 750°C a modified TbCu 7-type structure of space group P6/ mmm was found, in which the Fe(2 c) site is replaced by the partially (1/3) and randomly occupied Fe(6 l) site. Its approximate composition is SmFe 8.8–9.0. For T A between 800°C to 900°C a disordered modified Th 2Zn 17 structure (space group R 3 ̄ m) was found that is formed by introducing additional randomly occupied Fe (6 c) and Sm(3 a) positions, respectively. The degree of order of Sm atoms and Fe-dumbbells along the c-direction increases with increasing T A. A decrease in the Fe concentration in the cell is observed for increasing T A. The completely ordered stoichiometric Th 2Zn 17-type structure could not be reached by annealing samples prepared from the ball-milled elemental powders.