Solid compounds containing volatile elements often deviate from the stoichiometric composition, owing to the loss of the volatile species during thermal processes. This leads to a wide range of properties reported for the nominally same materials. It is important to understand how the process parameters of each fabrication step affect the volatility of the element, and how the physical properties change with the altered stoichiometry. Herein, we address this issue in n-type thermoelectric Bi2Te3-based alloys containing volatile Te. Thermal analysis indicated that mechanical deformation enhanced the volatility of Te by inducing a eutectic reaction through the formation of Te-rich phases. The effective evaporation of Te from the eutectic liquid phase created point defects and micropores, which significantly affected the thermoelectric and physical properties of the specimens. Moreover, Te atoms were transferred from heavily deformed samples to lightly deformed samples along the chemical potential gradients of Te via the vapor phase during annealing. The post-annealing temperature was increased above the eutectic temperature by introducing a pre-annealing step, which suppressed the formation of micropores. Therefore, we fabricated high-density n-type Bi2Te3-based alloys with a thermoelectric figure-of-merit (zTmax) of approximately 1.1, whose performance at the module level exceeded those of commercial single-crystal counterparts. This study provides a comprehensive relationship between the process parameters, Te volatility, and physical properties of Bi2Te3-based alloys. Our results offer an insight for the reproducibly and tuning of physical properties of other compounds containing volatile elements other than Bi2Te3.
|Journal||Journal of Alloys and Compounds|
|Publication status||Published - 2023 Mar 15|
Bibliographical noteFunding Information:
The authors gratefully acknowledge the financial support from National R&D Program ( 2022M3H4A1A04085311 ) and the Creative Materials Discovery Program ( NRF2020M3D1A111049911 ) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT.
© 2022 The Author(s)
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry