Thermal conductivity of solid solutions (Bi/sub y/Sb/sub 1-y/)/sub 2/Te/sub 3/ for y=0.7-0.8 grown by method of zone melting

Abstract

The linear deviation of concentration of excessive tellurium in the melt during zone melting C=C/sub o/(I+X/l), where C/sub o/ is the starting concentration of tellurium in the load, X is the zone co-ordinate on the ingot, and l is the length of the melting zone, is used for investigating the dependency of thermoelectric qualities of solid solutions (Bi/sub y/Sb/sub 1-y/)/sub 2/Te/sub 3/ on chemical composition distributed along the ingot. According to the distributed thermoelectric parameters obtained in the temperature range 150-360 K, the general projection of solidus line was made, depicting tellurium for solid solutions (Bi/sub y/Sb/sub 1-y/)/sub 2/Te/sub 3/ around the chemical composition with the melting temperature close to maximum. There exists a dependency of distribution of the thermoelectric parameters of the solid solutions along the ingot on the surface shape of their solidus. The distribution of remaining thermal conductivity, obtained as a result of subtraction of electron component, calculated on the basis of the Wiedemann Franz law, from the general one, calculated from the Seebeck coefficient figure of merit and electrical conductivity, depends on the ratio of atom parts of bismuth and antimony as well as on excessive concentration of tellurium in the melt. For y>0.5 around room temperature, the remaining thermal conductivity is an abrupt maximum corresponding to the area of intrinsic conductivity of the ingot The maximum of remaining thermal conductivity under y=0.7-0.8 and T=300K reaches the figure of 6.0/spl times/10/sup -2/ W/K/cm when at the same time the contribution of ambipole component of conductivity, according to the calculations, under this temperature is not above 6.0/spl times/10/sup -3/ W/K/cm. The most suitable mechanism, which can explain the anomalous increase of thermal conductivity in the solid solutions with chemical composition corresponding to the area where the solidus overlaps with stoichiometric cut, is transport of heat by excitons.