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Etude de skutterudites de terres-rares (R) et de métaux d (M) du type RM4Sb12 : de nouveaux matériaux thermoélectriques pour la génération d'électricité

Abstract : This thesis presents the physical and thermoelectric properties of new skutterudite compounds, with general formula Ry-pR'pFe4-x(Co/Ni)xSb12 (R et R' = Ce, Yb, Ba, La).
It shows that Yb valence state decreases when Yb fraction increases. However, it does not depend on the temperature, whiwh evidences a mixed valence state (two different valence states for two distinct cristallographic sites at a local point of view). Ce is always trivalent in these compounds. The character of the dominant interactions changes from antiferromagnetic to ferromagnetic when one goes from trivalent cerium or lanthanum to nearly divalent ytterbium or divalent baryum. The effective paramagnetic moment has been separated into three contributions originating from Ce, Yb and [Fe4Sb12]. The last one does not depend on the nature or on the valence state or R and R' atoms, but it decreases when Ni substitues Fe. A magnetic transition occurs at 6.5 K for R = Yb and Ba, possibly to a spin glass state.
Electrical and thermal transport properties have been determined from 5K to 800K, and the materials properties of the materials have been discussed concerning thermoelectric power generation. The power factor, and the thermoelectric figure of merit ZT are increased in Cey/2Yby/2Fe4-x(Co/Ni)xSb12 type skutterudites as compared to RyFe4-x(Co/Ni)xSb12 type skutterudites.
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Submitted on : Tuesday, May 31, 2005 - 4:51:17 PM
Last modification on : Thursday, January 11, 2018 - 6:14:36 AM
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David Bérardan. Etude de skutterudites de terres-rares (R) et de métaux d (M) du type RM4Sb12 : de nouveaux matériaux thermoélectriques pour la génération d'électricité. Matériaux. Université Paris XII Val de Marne, 2004. Français. ⟨tel-00009352⟩

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