CERMET COMPACT MADE FROM SEMICONDUCTING INSB WITH CONSTANT ELECTRICAL-RESISTANCE IN THE 4-400 K RANGE

A study of the electrophysical properties of samples prepared by phase transformation of stoichiometric InSb into InSb-Sb-In2O3 cermet compa ct has been performed (InSb, In2O3-semiconductors, antimony-metallic c onductivity). Samples were prepared by isothermal partial oxidation at 200-500 degrees C for 1-50 h. BuIk and thin-film samples annealed at 400 degrees C for 1-50 h possess relatively constant electrical resist ance over the wide temperature interval measured: 4-400 K. The convers ion degree, beta, and molar ratio, f = In2O3/2Sb were calculated from the isothermal thermogravimetry data according to the reaction equatio n 2InSb + 3/2O(2) = In2O3 + 2Sb at temperatures T < 400 degrees C, whe n no ascertainable amount of antimony is escaping from the system. The beta-value increases with temperature, T, and time of oxidation annea ling, t. However, instead of being constant, i.e. f = 0.5, f increases for T > 400 degrees C and t > 1 h. The X-ray powder diffraction, ther mogravimetry, differential thermogravimetry and differential thermal a nalysis measurements and studies revealed that metallic antimony escap es partially from the InSb-Sb-In2O3 system obtained at T greater than or equal to 400 degrees C. As a result, the mutual volume ratio of ind ividual InSb, Sb and In2O3 components is changed, and so also is the o verall character of the electrical resistivity of the samples. Due to the partial escape of Sb up arrow from the system at T greater than or equal to 400 degrees C, the following reaction is appropriate: 2InSb + 3/2O(2) = In2O3 + (2 - z) Sb up arrow = In2O3 f Sb/f + zSb, where z is the volatilized portion of Sb and fis the molar ratio of the reacti on products, i.e. f = In2O3/(2 - z)Sb = 1/(2 - z). The SEM observation s 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 in fluenced significantly, if instead of stoichiometric InSb, the initial In-Sb with a variable In/Sb ratio is used.