Attaining high mid-temperature performance in (Bi,Sb)2Te3 thermoelectric materials via synergistic optimization

For decades, zone-melted Bi2Te3-based alloys have been the most widely used thermoelectric materials with an optimal operation regime near room temperature. However, the abundant waste heat in the mid-temperature range poses a challenge; namely, how and to what extent the service temperature of Bi2Te3-based alloys can be upshifted to the mid-temperature regime. We report herein a synergistic optimization procedure for Indium doping and hot deformation that combines intrinsic point defect engineering, band structure engineering and multiscale microstructuring. Indium doping modulated the intrinsic point defects, broadened the band gap and thus suppressed the detrimental bipolar effect in the mid-temperature regime; in addition, hot deformation treatment rendered a multiscale microstructure favorable for phonon scattering and the donor-like effect helped optimize the carrier concentration. As a result, a peak value of zT of ~1.4 was attained at 500 K, with a state-of-the-art average zTav of ~1.3 between 400 and 600 K in Bi0.3Sb1.625In0.075Te3. These results demonstrate the efficacy of the multiple synergies that can also be applied to optimize other thermoelectric materials. A popular material for converting heat into electricity can now operate at elevated temperatures associated with industrial machinery. Bismuth tellurium is a thermoelectric alloy that works at room temperature and finds use in refrigeration and powergeneration, but much waste heat is created in the so-called middle temperature range of 100–300 degrees Celsius. Tiejun Zhu from Zhejiang University and colleagues doped indium atoms into bismuth tellurium to provide a balance to the excess, thermally activated charge carriers that normally materialize when this alloy is heated to middle temperatures. Hot deformations of the alloy during fabrication introduced missing-atom defects and micrograins that worked together with dopants to scatter heat-transporting phonon waves and optimize carrier concentrations. Thermoelectric and X-ray testing revealed that the doped alloyhad a higher working temperature and better mechanical properties. We herein report a synergistic optimization procedure that combines point defect engineering, band structure engineering and multiscale microstructuring in p-type (Bi,Sb)2Te3 thermoelectric materials by Indium doping and hot deformation. As a result, a peak value of zT ~1.4 was attained in Bi0.3Sb1.625In0.075Te3 at 500 K, along with a state-of-the-art average zTav of ~1.3 between 400 and 600 K. These results demonstrate the efficacy of the multi-synergies that can also be applied to optimize other thermoelectric materials.