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

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Phase equilibria studies are crucial for understanding material behavior at high temperatures.
• The Ta-V-Ge system is of interest for potential high-temperature applications.

Purpose of the Study:

• To determine the phase equilibria of the Ta-V-Ge system at 1500 °C for concentrations below 45 at% Ge.
• To characterize the crystal structures of ternary phases formed in the Ta-V-Ge system.

Main Methods:

• Alloys were prepared by argon arc melting and annealed at 1500 °C.
• Phase identification and characterization were performed using X-ray powder diffraction, electron probe microanalysis (EPMA), and transmission electron microscopy (TEM).
• Rietveld refinement was employed to determine the crystal structures of the ternary phases.

Main Results:

• Four ternary phases were identified in the isothermal section at 1500 °C.
• The phases include τ(1)-(Ta(1-x)V(x))(5)Ge(3) (Mn(5)Si(3)-type), τ(2)-Ta(Ta(x)V(1-x-y)Ge(y))(2) (MgZn(2)-type Laves phase), and τ(3)-Ta(9-x+y)V(4+x-y-z)Ge(1+z) (Nb(9)Co(4)Ge-type).
• A cubic Laves phase (C15-type) was stabilized by Ge addition, and V(11)Ge(8) exhibited extensive Ta solubility.

Conclusions:

• The phase diagram of the Ta-V-Ge system at 1500 °C was established for Ge concentrations <45 at%.
• New ternary phases and structure types were identified, expanding the knowledge of refractory metal germanides.
• The role of germanium in stabilizing specific crystal structures, such as Laves phases, was confirmed.