Simultaneous optimization of electrical and thermal transport properties of Bi0.5Sb1.5Te3 thermoelectric alloy by twin boundary engineering

The strong interdependence between the Seebeck coefficient, the electrical and thermal conductivity makes it difficult to obtain a high thermoelectric figure of merit, ZT. It is of critical significance to design a novel structure that manages to decouple these parameters. Here, we combine a liquid state manipulation method for solidified Bi0.5Sb1.5Te3 alloy with subsequent melt spinning, ball milling, and spark plasma sintering processes, to construct dedicated microstructures containing plenty of 60 degrees twin boundaries. These twin boundaries firstly scatter the very low-energy carriers and lead to an enhancement of the Seebeck coefficient. Secondly, they provide a considerable high carrier mobility, compensating the negative effect of the reduced hole concentration on the electrical conductivity. Thirdly, both experimental and calculated results demonstrate that the twin-boundary scattering dominates the conspicuous decrease of the lattice thermal conductivity. Consequently, the highest ZT value of 1.42 is achieved at 348 K, which is 27% higher than that of the sample with less twin boundary treated without liquid state manipulation. The average ZT value from 300 K to 400 K reaches 1.34. Our particular sample processing methods enabling the twin-dominant microstructure is an efficient avenue to simultaneously optimize the thermoelectric parameters.