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 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.