Thermoelectric property studies on Cu-doped n-type Cu _xBi ₂Te _2.7Se _0.3 nanocomposites

Combining high energy ball-milling and hot-pressing, significant enhancements of the thermoelectric figure-of-merit (ZT) have been reported for p-type Bi _0.4Sb _1.6Te ₃ nanocomposites. However, applying the same technique to n-type Bi ₂Te _2.7Se _0.3 showed no improvement on ZT values, due to the anisotropic nature of the thermoelectric properties of n-type Bi ₂Te _2.7Se _0.3. Even though texturing was effective in improving peak ZT of Bi ₂Te _2.7Se _0.3 from 0.85 to 1.04, reproducibility from batch to batch remains unsatisfactory. Here, we show that good reproducibility can be achieved by introducing an optimal concentration of 0.01 copper (Cu) per Bi ₂Te _2.7Se _0.3 to make Cu _0.01Bi ₂Te _2.7Se _0.3 samples. A peak ZT value of 0.99 was achieved in Cu _0.01Bi ₂Te _2.7Se _0.3 samples without texturing. With texturing by re-pressing, the peak ZT was increased to 1.06. Aging in air for over 5 months did not deteriorate but further improved the peak ZT to 1.10. The mechanism by which copper improves the reproducibility, enhances the carrier mobility, and reduces the lattice thermal conductivity is also discussed.