Theoretical and Experimental Study on Thermoelectric Properties of Ba8TM x Ga y Ge46–x–y (TM = Zn, Cu, Ag) T
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- 作者：Juliusz Leszczynski ; Andrzej Kolezynski…
- 关键词：Germanium clathrate ; thermoelectric materials ; thermal conductivity ; band structure ; WIEN2k ; DFT calculations
- 刊名：Journal of Electronic Materials
- 出版年：2016
- 出版时间：October 2016
- 年：2016
- 卷：45
- 期：10
- 页码：5264-5278
- 全文大小：2,307 KB
- 刊物类别：Chemistry and Materials Science
- 刊物主题：Chemistry
Optical and Electronic Materials
Characterization and Evaluation Materials
Electronics, Microelectronics and Instrumentation
Solid State Physics and Spectroscopy - 出版者：Springer Boston
- ISSN：1543-186X
- 卷排序：45
文摘
In the type I clathrates Ba8TMxGayGe46–x–y (TM = group 10 to 12 elements) where some of the Ge framework atoms are substituted by Zn, Cu or Ag, the transition-metal elements prefer to occupy the 6c site. Preliminary band-structure calculations showed that this substitution implies modification of the electronic bands in the vicinity of the energy gap. By appropriate tailoring of the band structure, improved thermoelectric properties can be obtained. More detailed full-potential linearized augmented plane wave (FP-LAPW) method calculations within density functional theory (DFT) were performed using the WIEN2k package for compositions where the transition element TM fully occupies the 6c site. Additional analysis of the properties of the electron density topology within Bader’s atoms-in-molecules approach was carried out to study the chemical bonding in intermetallic clathrates. To verify the theoretical predictions, polycrystalline samples of the type I clathrates Ba8TMxGayGe46–x–y (TM = Zn, Cu, Ag) modified by transition-metal element substitution for Ge were obtained. The samples were characterized using powder x-ray diffraction analysis, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. The electrical conductivity, Seebeck coefficient, and thermal conductivity were measured in the temperature range from 320 K to 720 K. Several models were used to fit the experimental results for the electronic transport properties and to estimate the energy gap. Vacancies at the Ge site were considered responsible for deviations from the desired properties, and appropriate defect equations correlating the vacancies and TM concentration are presented. Finally, the results of DFT calculations are compared with the experiments, showing good agreement with theoretically predicted cell parameters and general observations of the transport properties.