SUBSTITUTED W5SI3-TYPE AND ZR6AL2CO-TYPE PHASES FORMED IN THE ZIRCONIUM-ANTIMONY AND ZIRCONIUM-TIN SYSTEMS WITH IRON GROUP-METALS

Arc-melting and annealing reactions near the composition Zr5Sb3Fe yield ZrFe2 plus an Mn5Si3-type phase with a composition near Zr5Sb3.3Fe0.3. A lower antimony content and a variety of iron group metals produce tetragonal W5Si3-type phases with a narrow compositional range, ~Zr5Sb2.5T0.5, T = Fe, Co, Ni, Ru, Rh. A single-crystal study of the W5Si3-type Zr5Sb2.55(1)Fe0.45(1) established a mixed Sb-Fe population on the Sb1 site centering the Zr2 antiprisms (I4/mem, Z = 4, a = 11.066 (1) Å, c = 5.535 (1) Å, R/Rw = 1.9/2.8%). The analogous Zr-Sn-Fe system contains a W5Si3-like phase Zr5Sn2+xFe1–x, 0 ≤ x ≤ 0.28, but in this case with a lower symmetry tetragonal cell that has distinctly different mixed Fe-Sn populations centering adjacent Zr2 antiprisms (91 (2) and 52 (2)% Fe for x = 0.28) (I422, Z = 4, a = 11.1763 (7) Å, c = 5.4794 (6) Å, R/Rw = 1.7/2.2%). The lower symmetry cannot be deduced from powder pattern data. The hexagonal line phase Zr6Sn2Fe, previously known as the θ phase, is obtained when still more zirconium is present (Zr6Al2Co structure, P62m, Z = 1, a = 7.9675 (6) Å, c = 3.4863 (5) Å, R/Rw = 2.6/2.9%). Antimony systems provide analogous substitutional products ~Zr5Sb2.3T0.7, T = Fe, Co, Ni. Some regularities associated with the three structure types are discussed. © 1990, American Chemical Society. All rights reserved.