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

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.