Enhanced thermoelectric and mechanical performance of polycrystalline p-type Bi0.5Sb1.5Te3 by a traditional physical metallurgical strategy

In this paper, p-type Bi0.5Sb1.5Te3 polycrystalline materials have been fabricated by a traditional vacuum melting method, and the effects of cooling rate and MoSi2 addition on the microstructure, thermoelectric and mechanical performance of the polycrystalline materials have been studied detailedly. It shows that the amount of Te-rich eutectic phase increases and the lamellar microstructure has been refined with the increase of the cooling rate. Due to the combined effect of cooling rate on the carrier concentration and mobility, the air cooled sample has higher figure of merit than the furnace cooled, water cooled and liquid nitrogen cooled samples, and a maximal ZT of 1.02 at 50 degrees C was obtained for the air cooled polycrystalline sample. Under the same air cooling condition, the inhomogeneous nucleation sites increase with increasing the amount of MoSi2 particles, therefore the amount of Te-rich eutectic phase increases and the lamellar microstructure get refined, and the thermal conductivity of the sample decreases significantly due to the extra phonon scattering by the refined microstructure and MoSi2 particles. The resulted figure of merit Zr increases with increasing the amount of MoSi2 particles, and it decreases with further increasing the MoSi2 content after attaining the vertex of Zr = 1.33 at 100 degrees C at a content of 0.2 wt.% MoSi2. The flexural strength of the air cooled polycrystalline sample also increases with the amount of MoSi2 increasing from 0 to 0.3 wt.%, and a nearly 56% enhancement was achieved for the 0.2 wt.% MoSi2 sample (28.0 MPa) compared with the MoSi2 free sample. The improvement of flexural strength is in agreement with the Hall-Petch strengthening mechanism due to the lamellar microstructure refinement induced by MoSi2. (C) 2014 Elsevier Ltd. All rights reserved.