The system Ta–V–Si: Crystal structure and phase equilibria

Phase relations have been evaluated for the Ta–V–Si system at 1500 and 1200 °C. Three ternary phases were found: τ1-(Ta,V)5Si3 (Mn5Si3-type), τ2-Ta(Ta,V,Si)2 (MgZn2-type) and τ3-Ta(Ta,V,Si)2 (MgCu2-type). The crystal structure of τ2-Ta(Ta,V,Si)2 was solved by X-ray single crystal diffraction (space group P63/mmc). Atom order in the crystal structures of τ1-(Ta,V)5Si3 (Mn5Si3 type) and τ3-Ta(Ta,V,Si)2 was derived from X-ray powder diffraction data. A large homogeneity range was found for τ1-(TaxV1−x)5Si3 revealing random exchange of Ta and V at a constant Si content. At 1500 °C, the end points of the τ1-phase solution (0.082≤x≤0.624) are in equilibrium with the solutions (Ta1−xVx)5Si3 (Cr5B3 type, 0≤x≤0.128) and (TaxV1−x)5Si3 (W5Si3 type, 0≤x≤0.048).