Electronic and transport properties of polycrystalline Ba{sub 8}Ga{sub 15}Ge{sub 31} type I clathrate prepared by SPS method
- AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Silicate Chemistry and Macromolecular Compounds, Krakow (Poland)
- AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Inorganic Chemistry, Thermoelectric Research Laboratory, Krakow (Poland)
Samples of germanium Ba{sub 8}Ga{sub 15}Ge{sub 31} clathrate of type I were prepared using standard metallurgy methods. The structure, microstructure and phase composition of the prepared samples were analyzed by powder X-ray diffraction XRD and scanning electron microscope SEM combined with energy dispersive X-ray analysis EDX. Scanning thermoelectric microprobe STMP was used to characterize uniformity of Seebeck coefficient distribution at different stages of the material synthesis in order to optimize the synthesis method. Electrical conductivity, Seebeck coefficient and thermal conductivity were measured in the temperature range 20-450 Degree-Sign C. Based on the measured electrical properties and Hall carrier concentration n=5-9{center_dot}10{sup 20} cm{sup -3} at room temperature, electron effective mass m{sup Low-Asterisk} was estimated to be between 2.1-3 m{sub 0}. Preliminary FP-LAPW DFT calculations were performed for two chosen high symmetry superstructures Ba{sub 8}Ga{sub 16}Ge{sub 30} and Ba{sub 8}Ga{sub 6}Ge{sub 40} by means of WIEN2K package. Additionally topological analysis of total electron density according to Bader's Quantum Theory of Atoms in Molecules was carried out. The energy band gaps were calculated to be 0.3 eV for Ba{sub 8}Ga{sub 16}Ge{sub 30} and 0.38 eV for Ba{sub 8}Ga{sub 6}Ge{sub 40} which was close to the experimental results for Ba{sub 8}Ga{sub 16}Ge{sub 30}. The observed electrical properties were compared with the electronic band structure calculations, showing good qualitative correlation between the measured transport properties and the theoretical predictions. - Graphical abstract: Scanning thermoelectric microprobe STMP was used to investigate uniformity of the prepared polycrystalline Ba{sub 8}Ga{sub 15}Ge{sub 31} clathrate samples at different synthesis stages. Maps and histograms of the Seebeck coefficient distribution (presented in the picture) for Ba{sub 8}Ga{sub 15}Ge{sub 31} ingot after the first synthesis stage showed it is not uniform. The Seebeck coefficient distribution in the ingot was bimodal. The same analysis for the sample after annealing and sintering showed that the Seebeck coefficient distribution is unimodal. Compared to the ingot from I synthesis stage a significant improvement of material uniformity was observed. Highlights: Black-Right-Pointing-Pointer Scanning thermoelectric microprobe STMP measurements show important uniformity change during sample annealing. Black-Right-Pointing-Pointer Calculated band gap E{sub g} values are close to the reported E{sub g}. Black-Right-Pointing-Pointer Ga/Ge ratio change doesn't affect significantly the bonding properties. Black-Right-Pointing-Pointer Band structure calculations show that bond's character agrees with the Zintl concept.
- OSTI ID:
- 22149810
- Journal Information:
- Journal of Solid State Chemistry, Vol. 193; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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