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Article

Thermoelectric Properties and Microstructure of Ba₈Al₁₄Si₃₁ and EuBa₇Al₁₃Si₃₃

Cathie L. Condron,^† Susan M. Kauzlarich,*^† Franck Gascoin,^‡^§ and G. Jeffery Snyder^‡

Department of Chemistry, University of California Davis, One Shields Avenue, Davis, California 95616, and Materials Science, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125

Chem. Mater., 2006, 18 (20), pp 4939–4945

DOI: 10.1021/cm061483u

Publication Date (Web): September 7, 2006

†

University of California Davis.

To whom correspondence should be addressed. E-mail: smkauzlarich@ucdavis.edu.

‡

California Institute of Technology.

Current address: Laboratoire de Physico-Chimie de la Matière Condensée, Université Montpellier 2, place Eugène Bataillon, 34095 Montpellier Cedex 5, France.

Abstract

Powder samples of the type I clathrate phases, with the proposed stoichiometry Ba₈Al₁₆Si₃₀ and Eu₂Ba₆Al₁₆Si₃₀, were synthesized using direct reaction of stoichiometric amounts of the elements. Rietveld refinement of powder X-ray diffraction data is consistent with the clathrate type I structure. Composition, microstructure, and thermoelectric property measurements were made on hot-pressed pellets. Stoichiometry of the Ba₈Al₁₆Si₃₀ sample was determined from microprobe data to be Ba₈Al₁₄Si₃₁, close to the deficient framework solid solution of the general formula, Ba₈Al_xSi₄₂_-_3/4_x[]₄_-_1/4_x (x = 14; [], open square indicates lattice defect). In the case of the rare-earth-substituted compound, microprobe analysis of the microstructure indicates that it is not single phase, but contains multiple components, most of the general clathrate stoichiometry. The majority phase has the stoichiometry EuBa₇Al₁₃Si₃₂. Both phases show conductivity typical of heavily doped semiconductors with negative Seebeck coefficients. The highest Seebeck coefficients are − 99 and −71 μV/K at 1192 K for Ba₈Al₁₄Si₃₁ and EuBa₇Al₁₃Si₃₃, respectively. The maximum zT is 0.34 at 1150 K and 0.22 at 1165 K for Ba₈Al₁₄Si₃₁ and EuBa₇Al₁₃Si₃₃, respectively.