Improving Thermoelectric Properties of Inorganic Clathrates by Atomic and Microscale Structure Engineering
Doctoral thesis, 2021
In this thesis, we have studied the atomic and microscale structure of the clathrates and investigated its impact on the thermoelectric properties. Especially, with a combination of experiment and theoretical calculations, the existence of an order-disorder phase transition is confirmed. It further influences the electrical transport properties, since the band structure changes after the phase transition. The degree of chemical ordering can be controlled by the synthesis method, because materials reach different equilibrium states in either route. In addition, it is found that atomic vacancies can induce a peculiar transition effect in the electrical resistivity.
In order to investigate its influence on the thermoelectric performance, a novel method is employed, where Ba8(AlxGa1–x)16Ge30 clathrates are synthesized by alloying Ba8Al16Ge30 with Ba8Ga16Ge30. This way a heterostructure is created, which contains the quaternary clathrate main phase and aggregates of Al particles. Consequently, the charge carrier mobility is largely improved to a value higher than that of the single crystal, while the lattice thermal conductivity is reduced due to the enhanced phonon scattering at different length scales.
A greatly improved understanding of the process-structure-property relationship of clathrates is achieved in this thesis. The methodologies used, as well as the key findings, can be applicable for other material systems, and hence facilitate the future research in the thermoelectrics field.
Electrical transport properties
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Applied Surface Chemistry
Enhanced Thermoelectric Performance of Ba8Ga16Ge30 Clathrate by Modulation Doping and Improved Carrier Mobility
Advanced Electronic Materials,; Vol. 7(2021)
Order-Disorder Transition in Inorganic Clathrates Controls Electrical Transport Properties
Chemistry of Materials,; Vol. 33(2021)p. 4500-4509
Zhang Y., Brorsson J., Kamiyama T., Saito T., Erhart P., Palmqvist A. E. C. Investigating the Chemical Ordering in Quaternary Clathrate Ba8AlxGa16–xGe30.
Zhang Y., Brorsson J., Qiu R., Erhart P., Palmqvist A. E. C. Effect of Al/Ga Ratio on Atomic Vacancies Content and Thermoelectric Properties in Clathrates Ba8AlxGa16–xGe30.
Zhang Y., Palmqvist A. E. C. Effect of Ce Doping on the Thermoelectric Properties of Clathrates Ba8AlxGa16–xGe30.
Thermoelectric materials have been extensively studied: nanotechnology has boosted the thermoelectric performance of the state-of-art materials, the newly discovered materials have leveled the whole field to a more compelling state. In this thesis, we have studied inorganic clathrates, one of the prominent thermoelectric materials. Especially, we have investigated the atomic structure with a combination of experiment and theoretical calculation, and are able to tackle some problems that remained ambiguous previously. Moreover, by engineering the microstructure we have improved the thermoelectric performance of the clathrates. We believe that, the methodologies in this thesis are applicable to other materials systems and can facilitate the future research of thermoelectric materials.
Swedish Foundation for Strategic Research (SSF) (GSn15-0008), 2017-01-01 -- 2020-12-31.
Swedish Foundation for Strategic Research (SSF) (GSn15-0008), 2016-07-01 -- 2021-06-30.
Areas of Advance
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5042
Chalmers University of Technology
10:an, Kemigården 4, Chalmers. Zoom password: 548153
Opponent: Prof. Nini H. Pryds, Technical University of Denmark