Enhancement of thermoelectric properties in n-type Bi2Te3 through defect engineering via in situ NiTe2 precipitates

Abstract

Bi2Te3 composition serves as the parent compound of the highest performing thermoelectric materials at room temperature, including (Bi,Sb)2Te3, and Bi2(Te,Se)3. Herein, the thermoelectric transport properties of (Bi1-xNix)2Te3 (x = 0, 0.0075, 0.015, 0.03, 0.045, 0.06 and 0.075) compositions were systematically investigated by introducing Ni into the Bi2Te3 composition, which results in in-situ NiTe2 precipitates and Te-vacancies during synthesis. At low Ni contents (x = 0.0075 and 0.015), the electrical conductivity and power factor (PF) increase, while the lattice thermal conductivity (κlatt) concurrently decreases, yielding a broad enhancement of zT across 375–425 K with a peak near ∼450 K, compared with pristine Bi2Te3. Mechanistically, slight Te deficiency associated with NiTe2 formation introduces donor-type Te vacancies, increasing the carrier concentration (nH); a concurrent moderate rise in the density-of-states effective mass (md∗) supports higher weighted mobility and PF, whereas fine and numerous NiTe2 precipitates induce strong phonon scattering that sustains low κlatt. Consequently, both the thermoelectric quality factor (B) and zT are significantly elevated for x = 0.0075 and 0.015. In contrast, at higher Ni contents (x ≥ 0.03), self-compensation lowers nH, alloy/defect disorder grows, and NiTe2 coarsening partially recovers thermal conductivity and flattens the PF, shifting the zT maximum toward lower temperatures (∼350 K). This study demonstrates that combining reservoir-controlled defect chemistry with in-situ nanoscale precipitates is an effective strategy for improving Bi2Te3-based n-type thermoelectrics in the near-room-temperature regime.