Cermet compact made from semiconducting InSb with constant electrical resistance in the 4–400 K range

Abstract

A study of the electrophysical properties of samples prepared by phase transformation of stoichiometric InSb into lnSb-Sb-In₂O₃ cermet compact has been performed (InSb, In₂O₃-semiconductors, antimony-metallic conductivity). Samples were prepared by isothermal partial oxidation at 200–500°C for 1–50 h. Bulk and thin-film samples annealed at 400°C for 1–50 h possess relatively constant electrical resistance over the wide temperature interval measured: 4–400 K. The conversion degree, β, and molar ratio, f = In₂O₃/2Sb were calculated from the isothermal thermogravimetry data according to the reaction equation 2InSb+3/2O₂ = In₂O₃+2Sb at temperatures T < 400°C, when no ascertainable amount of antimony is escaping from the system. The β-value increases with temperature, T, and time of oxidation annealing, t. However, instead of being constant, i.e. f = 0.5, f increases for T > 400°C and t > 1 h. The X-ray powder diffraction, thermogravimetry, differential thermogravimetry and differential thermal analysis measurements and studies revealed that metallic antimony escapes partially from the InSb-Sb-In₂O₃ system obtained at T ≥ 400°C. As a result, the mutual volume ratio of individual InSb, Sb and In₂O₃ components is changed, and so also is the overall character of the electrical resistivity of the samples. Due to the partial escape of Sb↑ from the system at T ≥ 400°C, the following reaction is appropriate: 2InSb + 3/2O₂ = In₂O₃ + (2 − z) Sb↑ = In₂O₃+Sb/f+ zSb, where z is the volatilized portion of Sb and f is the molar ratio of the reaction products, i.e. f = In₂O₃/(2 − z)Sb = 1/(2 − z). The SEM observations revealed a growing grain size with temperature and time of annealing, lowering the grain-boundary density and thus also the resistivity of the samples. The properties of the obtained ternary compact may be influenced significantly, if instead of stoichiometric InSb, the initial In-Sb with a variable In/Sb ratio is used.