Issue 20, 2012

Phase relations and crystal structures in the system Ta–V–Ge

Abstract

Phase equilibria have been derived for the isothermal section of the Ta–V–Ge system at 1500 °C (for concentrations <45 at% Ge) on the basis of X-ray powder diffraction, EPMA and TEM analyses of argon arc melted alloys annealed in high vacuum at 1500 °C up to 200 hours. Four ternary phases have been identified within the isothermal section, out of which three were characterized by Rietveld refinement of X-ray powder diffraction data. τ1-(Ta1−xVx)5Ge3 (0.21 ≤ x ≤ 0.63) adopts the Mn5Si3-type and τ2-Ta(TaxV1−xyGey)2, x = 0.02, y = 0.12 was found to be a MgZn2-type Laves phase. Detailed transmission electron microscopy (TEM) in several crystallographic directions confirmed lattice parameters and crystal symmetry of this phase and rejected the presence of any superstructure. τ3-Ta9−x+yV4+xyzGe1+z, x = 0.32, y = 0.51, z = 0.98 crystallizes with the Nb9Co4Ge-type, whereas the structure of τ4 is not yet known. Although a MgCu2-type cubic Laves phase is not present in the Ta–V binary at this temperature, additions of Ge stabilize this phase in the ternary system: C15-Ta(TaxV1−xyGey)2, x = 0.04, y = 0.05. V11Ge8 (Cr11Ge8 type) shows a large solubility up to (TaxV1−x)11Ge8, x = 0.64 at 1500 °C.

Graphical abstract: Phase relations and crystal structures in the system Ta–V–Ge

Article information

Article type
Paper
Submitted
20 Dec 2011
Accepted
07 Mar 2012
First published
08 Mar 2012

Dalton Trans., 2012,41, 6206-6214

Phase relations and crystal structures in the system Ta–V–Ge

A. U. Khan, J. Bursik and P. Rogl, Dalton Trans., 2012, 41, 6206 DOI: 10.1039/C2DT12455F

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