Berlin 2012 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 32: Thermoelectric materials I (Focused session – Organizers: Meyer, Heiliger)

DS 32.1: Hauptvortrag

Donnerstag, 29. März 2012, 09:30–10:00, H 2032

Tuning thermoelectric properties of oxides by the interplay between spin/charge/lattice — •Sylvie Hebert — Laboratoire CRISMAT UMR6508 CNRS et ENSICAEN

Following the discovery of a large thermopower in NaxCoO2 with x ~ 0.7 [I. Terasaki et al., PRB56, R12685 (1997)], the thermoelectric properties of oxides have been intensively investigated in the last 10 years. The presence of strong correlations in these materials could be a way to enhance the thermopower, and low dimensional structures could also be beneficial. Moreover, these materials present fascinating properties beyond thermoelectricity, as superconducting properties appearing in the hydrated phase with x ~ 0.3, showing the richness of their phase diagram.

For p type oxides, the most interesting materials are layered compounds deriving from NaxCoO2, with layers of edge shared CoO6 octahedra, with a mixed valency of Co3+ and Co4+ in low spin states located on a triangular lattice. Following these results, we have been investigating several families of oxides, p or n type, to better understand the interplay between the crystallographic structure, the different spin and valence states, and the thermopower. In this presentation, several examples will be presented emphasizing the relative influence of electronic correlations, and spin and orbital degeneracies in these oxides.