Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

The guest framework interactions and the oxidation state (valency) of guest atoms in type I inorganic clathrates

First principles DFT methods, using local gaussian basis sets, were applied to calculate the electronic structure of type I inorganic clathrates ( Sr(8)Ga(16)Ge(30), Ba(8)Ga(16)Ge(30) ). A careful tuning of the basis set enabled us to consider crystal groups with low or no symmetry, corresponding to different sittings for the Ge and Ga atoms. Use of the Quantum Theory of Atoms in Molecules (QTAM) on the resulting wave functions allowed us to put the guest-host interactions on a physically sound basis.

The charge transfer from guests to the semi-conducting framework was obtained by integrating the charge within the guest basins, using the QTAM recipe, which is firmly rooted in quantum mechanics. The result is freed from any arbitrariness, at variance with estimates from other approaches (X-ray adsorption, magnetic measurements, etc.).

Contrary to previous experimental and theoretical estimates, the guest atoms are found to be mostly ionic. We fully reconciled theory with the Zintl phase view that structural chemists have of these systems. We show this discrepancy to be related to wrong definitions used for electron transfer.

Preliminary investigations ruled out any important relationship between the observed increase in the thermoelectric figure of merit with increasing external pressure, and the host-guest charge transfer.

More information on the NANOTHERMEL project can be found at:

Reported by

Italian National Research Council
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