Constitution of the systems {V,Nb,Ta}-Sb and physical properties of di-antimonides {V,Nb,Ta}Sb-2

The binary phase diagrams {V,Nb,Ta}-Sb below 1450 °C were studied by means of XRPD, EPMA, and DTA measurements. In the V-Sb system, five stable binary phases were observed in this investigation: V _3+xSb _1-x, →T-V ₃Sb ₂, hT-V _2-xSb, V _7.46Sb ₉, V _1-xSb ₂. The V-Sb phase diagram is characterized by two degenerate eutectic reactions: L→V _3+xSb _1-x+(V) (T > 1450 °C at 18.1 at.% Sb) and LV _1-xSb ₂+(Sb) (T=(621 ± 5)°C at ∼99 at.% Sb), three peritectic reactions: L + V _3+xSb _1-x+hT-V _2-xSb (T=(1230 ± 10)°C at ∼42 at.% Sb), L + hT-V _2-xSb+V _7.46Sb ₉ (T=(920 ± 10)°C at ∼87 at.% Sb), and L + V _7.46Sb ₉+V _1-xSb ₂ (T=(869 ± 5)°C at ∼88 at.% Sb), a peritectoid reaction: V _3+xSb _1-x + hT-V _2-xSb→T-V ₃Sb ₂ at (875 ± 25)°C, a eutectoid reaction: hT-V _2-xSb →T-V ₃Sb ₂+V _7.46Sb ₉ at (815 ± 15)°C and congruent melting of V _3+xSb _1-x (T > 1450 °C). An X-ray single crystal study of V ₅Sb ₄C _1-x proved the existence of interstitial elements in the octahedral voids of a partially filled Ti ₅Te ₄-type structure (x∼0.5; R _F2 = 0.0101), therefore this phase (earlier labeled "V ₅Sb ₄") was excluded from the binary equilibrium phase diagram. V ₅Sb ₄C _1-x is the first representative of a filled Ti ₅Te ₄-type structure. A re-investigation of the Nb-Sb system removed the contradiction between the hitherto reported phase diagrams and confirmed the version derived by Melnyk et al. (see ref. [1]). Three binary phases exist in the Ta-Sb system: Ta _3+xSb _1-x, Ta ₅Sb ₄, TaSb ₂. Due to instrumental limits (<1450 °C), only the peritectic reaction of TaSb L + Tab+ TaSb ((1080 ± 10)°C at ∼92 at.% Sb) and a degenerate Sb-rich eutectic reaction (L+TaSb (622 ± 5)° ∼99 at.% Sb) have been determined. Physical properties (mechanical and transport properties) of binary di-antimonides were investigated with respect to a potential use of these metals either as diffusion barriers or electrodes for thermoelectric devices based on skutterudites. All group-V metal di-antimonides have low metallic-type resistivity and relatively high thermal conductivity. Magnetic field has little influence on the resistivity of V at low temperature, while on {Nb,Ta}Sb it increases the resistivity, especially on NbSb The coefficient of thermal expansion (CTE) decreases from V to TaSb, particularly the CTE value of NbSb is in the range of average n-type filled skutterudites. In contrast to the CTE value, elastic moduli increase from V to TaSb. The value for V is in the range of Sb-based skutterudites, whereas the values for {Nb,Ta}Sb are significantly higher.