The antimony-niobium (Sb-Nb) system

A constitutional diagram was established for the Nb-Sb system in the region with more than 30 at. % Sb and below 1450 °C. Investigation of the phase relations was based on differential thermal analysis (DTA), light optical microscopy, electron probe microanalysis, and X-ray diffraction experiments on argon arc melted bulk alloys, which were annealed at 600 °C in vacuum-sealed silica capsules up to 1400 h. Differential thermal analysis runs (5 to 20 K/min, T _max=1450 °C) were performed on alloys vacuum sealed in Ta crucibles with an inner lining of W. In contrast to earlier claims for the existence of five binary phases, Nb₃Sb, Nb₃Sb₂, NbSb, Nb₅Sb₄ (or Nb₄Sb₃), and NbSb₂, the authors observed only three binary compounds: Nb₃Sb, Nb₅Sb₄, and NbSb₂. These compounds are essentially line compounds at their stoichiometric composition and without a significant homogeneity region at 600 °C. All compounds are formed by peritectic reactions: L+(Nb)↔Nb₃Sb (1750±25 °C, (L℞55 at.% Sb), L+Nb₃Sb↔Nb₅Sb₄ (1320±10 °C, L℞71 at.% Sb), and L+Nb₅Sb₄↔NbSb₂ (1180±10 °C, L℞88 at.% Sb). The system is characterized by a depleted eutectic reaction L↔(Sb)+NbSb₂ at 618±8 °C and L℞99 at.% Sb.