Mechanically enhanced p- and n-type Bi2Te3-based thermoelectric materials reprocessed from commercial ingots by ball milling and spark plasma sintering

Ball milling (BM) combined with spark plasma sintering (SPS) is increasingly used for fabricating high-performance thermoelectric materials. This work was conducted to clarify the effects of BM and SPS on the electrical transport and thermoelectric properties of both p- and n-type Bi2Te3 based materials using commercially available p-type (Bi,Sb)2Te3 and n-type Bi2(Se,Te)3 ingots. Interestingly, it is found that BM and SPS differently affected the electrical properties of p- and n-type Bi2Te3-based thermoelectric materials; the dimensionless thermoelectric figure of merit (ZT) increases in p-type Bi0.5Sb1.5Te3 but decreases somewhat in n-type Bi2Te2.7Se0.3 after BM and SPS. Hall experiments reveal the reason for this difference. Both p-type and n-type sintered materials show 2-3 times higher mechanical strength than the ingots because of microstructure refinement effect, which has been measured by using a small-sized biaxial bending test. The improved mechanical properties are in favor for device fabrication.