THERMOELECTRIC PROPERTIES OF Bi₂Te₃–Sb₂Te₃ ALLOYS

Alloys of nominal composition Bi 2−x Sb x Te 3+y were prepared in an evacuated, sealed ampule by a horizontal zone melting method. Single-crystal samples were cut from the ingots, and measurements of Seebeck coefficient, electrical conductivity, thermoelectric figure of merit (Z), and thermal conductivity (κ) were made over a temperature range of 160 to 360 °K using the Peltier–Seebeck method developed by Harman. Alloys of nominal composition Bi 2−x Sb x Te 3 . 13 were found to be n type for [Formula: see text] and p type for x > 1. In alloys of high antimony content, the hole concentration was influenced very little by the amount of excess tellurium. The change of Z was studied by varying y from 0.06 to 0.26 at x equal to 0, 0.25, 1.4, 1.5, and 1.6 respectively. Optimum doping to maximize Z did not appear to be possible in a simple way over the entire range of x between 0 and 2. The temperature dependence of κ indicated that the maximum Z at x = 1.5 may be limited by an ambipolar contribution.