Influence of Growth Conditions and Tellurium Phase on the Thermoelectric Properties of Bismuth Telluride-Type Materials

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Abstract
A study has been made in n-type Bi2Te3+x, n-type Bi2Se0.45Te3+x, and p-type Bi0.5Sb1.5Te3+x of the influence of segregated tellurium phase, determined metallographically, on the thermoelectric figure of merit (Z), electrical conductivity (σ), Seebeck coefficient (α), and thermal conductivity (κ). It was found that Z and σ at a given α value were reduced by excessive amounts of the Te phase. Calculation using an idealized two-phase model has shown that in this case circulating currents are unimportant. The effects appear to be due to a redistribution of electrical and thermal current by the Te phase located mostly between cleavage planes where any misalignment can have a strong influence. Zone melting of p-type Bi0.5Sb1.5Te3.13 at low speeds of about 0.1 cm/h produced an increase in the average value of Z and a decrease in the amount of Te phase.