The ternary system: silicon–uranium–vanadium

Phase equilibria in the system Si–U–V were established at 1100 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed, U2V3Si4 and (U1−xVx)5Si3, for which the crystal structures were elucidated by X-ray powder data refinement and found to be isotypic with the monoclinic U2Mo3Si4-type (space group P21/c; a = 0.6821(3), b = 0.6820(4), c = 0.6735(3) nm, β = 109.77(1)°) and the tetragonal W5Si3-type (space group I4/mcm, a = 1.06825(2), c = 0.52764(2) nm), respectively. (U1−xVx)5Si3 appears at 1100 °C without any significant homogeneity region at x ∼ 0.2 resulting in a formula U4VSi3 which corresponds to a fully ordered atom arrangement. DTA experiments clearly show decomposition of this phase above 1206 °C revealing a two-phase region U3Si2 + V3Si. At 1100 °C U4VSi3 is in equilibrium with V3Si, V5Si3, U3Si2 and U(V). At 800 °C U4VSi3 forms one vertex of the tie-triangle to U3Si and V3Si. Due to the rather high thermodynamic stability of V3Si and the corresponding tie-lines V3Si + liquid at 1100 °C and V3Si + U(V) below 925 °C, no compatibility exists between U3Si or U3Si2 and vanadium metal.