Ultralow Lattice Thermal Conductivity and Improved Thermoelectric Performance in Cl-Doped Bi2Te3- xSex Alloys

Taras Parashchuk; Rafal Knura; Oleksandr Cherniushok; Krzysztof T Wojciechowski

doi:10.1021/acsami.2c08686

Ultralow Lattice Thermal Conductivity and Improved Thermoelectric Performance in Cl-Doped Bi₂Te_{3- x}Se_x Alloys

ACS Appl Mater Interfaces. 2022 Jul 13;14(29):33567-33579. doi: 10.1021/acsami.2c08686. Online ahead of print.

Authors

Taras Parashchuk¹, Rafal Knura^{1

2}, Oleksandr Cherniushok¹, Krzysztof T Wojciechowski¹

Affiliations

¹ Thermoelectric Research Laboratory, Department of Inorganic Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Mickiewicza Ave. 30, Krakow 30-059, Poland.
² Department of Science, Graduate School of Science and Technology, Kumamoto University, 2 Chome-39-1 Kurokami, Chuo Ward, Kumamoto 860-8555, Japan.

Abstract

Bi₂Te₃-based alloys are the main materials for the construction of low- and medium-temperature thermoelectric modules. In this work, the microstructure and thermoelectric properties of Cl-doped Bi₂Te_3-xSe_x alloys were systematically investigated considering the high anisotropy inherent in these materials. The prepared samples have a highly oriented microstructure morphology, which results in very different thermal transport properties in two pressing directions. To accurately separate the lattice, electronic, and bipolar components of the thermal conductivity over the entire temperature range, we employed a two-band Kane model to the Cl-doped Bi₂Te_3-xSe_x alloys. It was established that Cl atoms act as electron donors, which tune the carrier concentration and effectively suppress the minority carrier transport in Bi₂Te_3-xSe_x alloys. The estimated value of the lattice thermal conductivity was found to be as low as 0.15 Wm^-1 K^-1 for Bi₂Te_3-x-ySe_xCl_y with x = 0.6 and y = 0.015 at 673 K in parallel to the pressing direction, which is among the lowest values reported for crystalline materials. The large reduction of the lattice thermal conductivity in both pressing directions for the investigated Bi₂Te_3-xSe_x alloys is connected with the different polarities of the Bi-(Te/Se)1 and Bi-(Te/Se)2 bonds, while the lone-pair (Te/Se) interactions are mainly responsible for the extremely low lattice thermal conductivity in the parallel direction. As a result of the enhanced power factor, suppressed bipolar conduction, and ultralow lattice thermal conductivity, a maximum ZT of 1.0 at 473 K has been received in the Bi₂Te_2.385Se_0.6Cl_0.015 sample.

Keywords: anisotropy; bipolar conduction; bismuth telluride; bonding inhomogeneity; lone-pair electrons; thermoelectric properties; two-band Kane model.