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Synthesis and crystal structure investigations of Ge based clathrates

In the present result we have carried out zone refinement synthesis and thermoelectric property characterization on Ge based clathrates. Melt/solid distribution coefficients have been determined for a large number of dopant atoms in Ba(8)Ga(16)Ge(30). We have furthermore shown that very accurate control of the composition is the key to controlling the thermoelectric properties.

The crystal structures have been investigated with state of the art synchrotron radiation techniques and analysis of single crystal diffraction data. In particular, we have developed a new experimental method to obtain site selective valence information on the nanoinclusions in the system. We have used a different approach than in the typical DAFS experiment. Instead of collecting few reflections at many different wavelengths, we have collected many reflections at relatively few wavelengths around the Sr k-edge. This allows us to obtain the anomalous scattering component directly as a parameter in the crystallographic refinements. This anomalous scattering contains the information on the guest atom valence state.

One key result is the finding that guest inclusions in Ge based clathrates are ionic and thus conform with the Zintl view of these solids. This aspect has been debated in the literature.

More information on the NANOTHERMEL project can be found at:

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