Synergistic tuning of carrier and phonon scattering for high performance of n-type Bi2Te2.5Se0.5 thermoelectric material

Polycrystalline Bi2Te2.5Se0.5 materials with different amounts of added MnTe2 have been fabricated by plasma activated sintering. XRD, SEM, EDS and HRTEM techniques and measurements of the electrical and thermal transport properties have been employed to study the effect of MnTe2 addition on the microstructure and the thermoelectric performance of Bi2Te2.5Se0.5 materials. Due to the substitution of Mn at the Bi sites, the XRD peaks shift towards a higher angle with an increase in the content of MnTe2, and the electron density increases; thus, the bipolar conduction is suppressed and accordingly shifts to a higher temperature. When the content of MnTe2 is over 3.0 at%, the dissolution of MnTe2 gets saturated, and some nanoinclusions with sizes of about 40-70 nm were observed and were identified as MnTe2 by EDS and HRTEM characterization. Due to the extra phonon scattering by the Mn-Bi' point defects and MnTe2 nanoinclusions, the phonon thermal conductivity decreased significantly. As a result, a maximum ZT of 1.0 at 523 K was achieved in the sample with 3.0 at% MnTe2, which is about a 150 K degree shift and a 100% improvement at this temperature compared with the conventional n-type Bi2Te3-based materials.