Thermal Stability and Phase Purity in Polycrystalline Ba8Ga x Ge46−x
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Polycrystalline Ba8Ga x Ge46−x exhibits promising thermoelectric performance with the figure of merit ZT close to that of single crystals. Polycrystalline Ba8Ga x Ge46−x is promising for applications, but reproducibility and thermal stability of thermoelectric properties need to be demonstrated. Polycrystalline samples of Ba8+dGa x Ge46−x -type clathrates (15.0 ≤ x ≤ 16.8 with varied nominal Ga content and d = 0 or 0.2) were prepared by direct reaction of the elements, followed by ball milling and hot pressing. Trace Ge impurity was observed (<1.0 wt.%) depending on the synthesis method. The electrical resistivity was stable in measurements up to 1000 K, regardless of Ge impurity. However, measurements to 1050 K resulted in irreversible increase in carrier concentration while the carrier mobility remained unchanged.
KeywordsClathrate electrical resistivity carrier concentration Ba8Ga16Ge30 thermoelectricity
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The Beckman Institute at Caltech, the Swedish Bengt Lundqvist Minne Foundation, and JPL-NASA are greatly acknowledged for financial support.
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