The antimony-iron-zirconium (Sb-Fe-Zr) system

Abstract

Phase equilibria were established in the Fe-Sb-Zr ternary system below 60 at.% Sb for an isothermal section at 800 °C; the very Sb-rich region was studied at 600 °C. Investigation of the phase relations was based on light optical microscopy, electron probe microanalysis, and X-ray diffraction experiments on arc melted bulk alloys, which were annealed up to 350 h. Three ternary compounds were observed: ZrFe1−x Sb (0.3<x<0.5; defect TiNiSi Type), Zr6Fe1−x Sb2+x (0<x<0.24; ordered Fe2P type) and Zr5Fe x Sb3−x (x=0.44; W5Si3 type). Whereas Zr5Fe0.44Sb2.56 at 800 °C formed at a given composition without a significant homogeneity region, a rather extended solid solution up to about 9 at.% Sb was observed for the Laves phase Zr(Fe1−x Sb x )2−y . At 800 °C, binary ZrFe2−y was only observed with the cubic MgCu2 type; Sb content of more than about 3 at.% Sb stabilized the hexagonal MgNi2 type in the Zr-poor end of the homogeneity region. The MgCu2 type prevails at higher Sb content of up to 9 at.% Sb at the Zr-rich side. Zr3Sb (Ni3P type) seems to dissolve up to 3.5 at.% of Fe replacing Zr in the structure. Binary Zr5Sb3+x (Ti5Ga4 type or filled Mn5Si3 type) dissolves up to 11 at.% Fe by gradually replacing the Sb atoms in the octahedral sites with Fe; thus the boundary of the homogeneous region on the Fe-rich side essentially corresponds to the ternary limit at Zr5FeSb3. For stoichiometric binary Zr5Sb3 the authors observed only a small solubility (<1 at.% Fe) with the Yb5Sb3 type. At 800 °C there is practically no solid solubility of Zr in the iron antimonides and of Fe in the zirconium antimonides richer than 40 at.% Sb.