THERMOELECTRIC PROPERTIES OF n-TYPE Bi2Te3–Bi2Se3 ALLOYS

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Abstract
Room temperature measurements of the Seebeck coefficient (α), electrical conductivity (σ), thermal conductivity (κ), and thermoelectric figure of merit (Z) were made on samples of n-type Bi2Te3–Bi2Se3 pseudobinary alloys over the whole composition range. To obtain maximum Z, doping was carried out at each composition by the addition of CuBr (donor) from 0 to 66 mole% Bi2Se3 and by lead and excess Se (acceptors) thereafter. Experimentally determined values of the materials parameter β were found to saturate (β∞) at high conductivity in a given alloy and close relationship was found between β∞ and Zmax The optimized values of σ, κ, and CuBr-dopant concentration were found to show a maximum at 33 mole% Bi2Se3, while the optimized value of α showed a minimum at this composition. These results, together with the fact that no maximum was observed in σ at constant α (i.e., constant carrier concentration), suggest that a maximum in the carrier concentration occurs in optimized material at this composition. Further support for this was provided by the observed variation of σ with α at a given composition which was found to be more consistent with a minimum in the apparent energy gap near 33% Bi2Se3 rather than the maximum reported by other workers.