The niobium (columbium)-platinum constitution diagram

The Nb-Pt system was investigated over the entire composition range by metallography and X-ray diffraction analysis. The solubility limits of terminal and intermediate phases and solidus temperatures were determined. α-Nb dissolves ≈12 at. pct Pt at 2040 °C and ≈5 at. pct Pt at 1150 °C; α-Pt dissolves ≈20 at. pct Nb at 2000 °C and ≈ 18 at. pct Nb at temperatures below 1700 °C. The presence of six intermediate phases, Nb₃Pt (Cr₃O, A15 or β-W type), σ(≈Nb₂Pt, β-U type), Nb_1−xPt_1+x (AuCd type), α′-Pt (undetermined structure), NbPt₂ (MoPt₂ type), α-NbPt₃ (TiCu₃ type), and β-NbPt₃ (β-NbPt₃ type) was confirmed. The phase NbPt₃ melts congruently at ≈2040 °C, and σ forms peritectically at ≈1800 °C. By analogy with related systems, the high-temperature phase α′-Pt is probably an extension of and isomorphous with α-Pt solid solution. Eight three-phase reactions are described, the mean atomic volumes are given, and crystal chemical relationships among the six homologous T₅-T₁₀ systems (T₅ = V, Nb, Ta; T₆ = Pd, Pt) are discussed.