Multiple Roles of Unconventional Heteroatom Dopants in Chalcogenide Thermoelectrics: The Influence of Nb on Transport and Defects in Bi2Te3 (original) (raw)

Improvements in the thermoelectric performance of n-type Bi 2 Te 3 materials to more closely match their p-type counterparts are critical to promote the continued development of bismuth telluride thermoelectric devices. Here the unconventional heteroatom dopant, niobium, has been employed as a donor in Bi 2 Te 3. Nb substitutes for Bi in the rhombohedral Bi 2 Te 3 structure, and exhibits multiple roles in its modulation of electrical transport and defect-induced phonon 2 scattering. The carrier concentration is significantly increased as electrons are afforded by aliovalent doping and formation of vacancies on the Te sites. Further, incorporation of Nb in the pseudo-ternary Bi 2-x Nb x Te 3-δ system increases the effective mass, m*, which is consistent with cases of "conventional" elemental doping in Bi 2 Te 3. Lastly, inclusion of Nb induces both point and extended defects (tellurium vacancies and dislocations, respectively), enhancing phonon scattering and reducing the thermal conductivity. As a result, an optimum zT of 0.94 was achieved in n-type Bi 0.92 Nb 0.08 Te 3 at 505 K, which is dramatically higher than an equivalent undoped Bi 2 Te 3 sample. This study suggests that not only is Nb an exciting and novel electron dopant for the Bi 2 Te 3 system, but also that unconventional dopants might be utilized with similar effects in other chalcogenide thermoelectrics.