Improvement of power factor of n-type Bi2Te3 by dispersed nanosized Ga2Te3 precipitates

Inspired by the concept of energy filtering effect in improving the thermoelectric power factor (PF), we introduced a nanosized filter phase in an n-type Bi2Te3 bulk material. We selected Ga2Te3 as the filter phase because it has a suitable band offset at the conduction band minimum, as predicted by the first-principles calculations. We synthesized Bi2Te3 containing Ga2Te3 precipitates by carefully controlling the sintering and annealing temperatures, which followed the liquid-quenching process. It was found that the nanosized Ga2Te3 precipitates (∼100 nm) improved the PF of n-type Bi2Te3, while the microsized Ga2Te3 did not. In particular, the homogeneously dispersed nanosized Ga2Te3 precipitates were better than the segregated Ga2Te3 at the grain boundaries in improving the PF. The obtained PF of Bi1.9Ga0.1Te3 at 300 K was 2.80 × 10−3 W/mK2, which is 60% higher than that of n-type Bi2Te3. The Jonker plot clearly showed that this improvement is far beyond the optimized value for the given carrier concentration.