| Autor: |
Bryan, J. Daniel, Blake, Nick P., Metiu, Horia, Stucky, Galen D., Iversen, Bo B., Poulsen, Rasmus D., Bentien, Anders |
| Předmět: |
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| Zdroj: |
Journal of Applied Physics; 12/15/2002, Vol. 92 Issue 12, p7281, 10p, 1 Black and White Photograph, 7 Charts, 5 Graphs |
| Abstrakt: |
Zone melting purification experiments have been carried out on the clathrate, Ba[sub 8]Ga[sub 16]Ge[sub 30]. The impurities present have been identified and their approximate concentrations measured. Trace impurities were determined to be approximately 240 parts per million (ppm) in the most impure sample to 17 ppm in the most pure sample. The temperature-dependent Seebeck coefficient, thermal conductivity, and electrical conductivity are reported as a function of sample purity as well as the room-temperature Hall coefficient. Microprobe analysis suggests that the samples are nonstoichiometric with excess Ge relative to Ga, and there are indications of the presence of defects. Single-crystal x-ray investigations as well as synchrotron powder diffraction measurements support the presence of defects, but the x-ray data cannot accurately determine the relative amounts of Ga and Ge. Band-structure calculations in the generalized gradient approximation show that the measured Hall and Seebeck coefficients are consistent with a defect lattice of approximate stoichiometry Ba[sub 8]Ga[sub 14]Ge[sub 31]. Although the figure of merit (ZT) is found to be the highest for the purest sample, the dominant contribution to transport is conjectured to arise from deviations from the ideal stoichiometry and not impurities. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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