Ultrasonic-assisted hot pressing of Bi2Te3-based thermoelectric materials.

Abstract In this study, n -type Bi 2 Te 3 -based bulk materials were prepared using the ultrasonic-assisted hot pressing. The effects of ultrasonic vibration on the mechanical and thermoelectric properties of the prepared samples were investigated. Field-emission scanning electron microscope (FESEM) tests revealed that the ultrasonic vibration refined the grain size to the submicron level. The grain size became smaller as the ultrasonic vibration duration is extended. The results showed that the sample with an ultrasonic vibration duration of 20 min (namely, Ultra 20) has a hardness of 64 HV0.3 and a flexural strength of 22.4 MPa, which represents an 82.9% and 50.2% improvement, respectively, over the untreated hot-pressed sample (namely, Ultra 0). As the ultrasonic vibration duration increased, the absolute value of the Seebeck coefficient was found to increase, whereas the electrical conductivity and the thermal conductivity decreased. The maximum dimensionless figure of merit (ZT max) was 0.78 at 480 K for the Ultra 20 sample, which was 10.9% and 16.4% higher than the Ultra 10 and Ultra 0 samples, respectively. The results proved that both the mechanical properties and the thermoelectric properties of the Bi 2 Te 2.7 Se 0.3 bulk materials are improved by ultrasonic vibration. [ABSTRACT FROM AUTHOR]