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Issue 20, 2012
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Phase relations and crystal structures in the system Ta–V–Ge

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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

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Publication details

The article was received on 20 Dec 2011, accepted on 07 Mar 2012 and first published on 08 Mar 2012


Article type: Paper
DOI: 10.1039/C2DT12455F
Citation: Dalton Trans., 2012,41, 6206-6214
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    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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