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Title: Crystal structure, characterization and thermoelectric properties of the type-I clathrate Ba{sub 8-y}Sr{sub y}Al{sub 14}Si{sub 32} (0.6{<=}y{<=}1.3) prepared by aluminum flux

The title compound was prepared as single crystals using an aluminum flux technique. Single crystal and powder X-ray diffraction indicate that this composition crystallizes in the clathrate type-I structure, space group Pm3-bar n. Electron microprobe characterization indicates the composition to be Ba{sub 8-y}Sr{sub y}Al{sub 14.2(2)}Si{sub 31.8(2)} (0.77<y<1.3). Single-crystal X-ray diffraction data (90 and 12 K) were refined with the Al content fixed at the microprobe value (12 K data: R{sub 1}=0.0233, wR{sub 2}=0.0441) on a crystal of compositions Ba. The Sr atom preferentially occupies the 2a position; mixed Al/Si occupancy was found on all framework sites. These refinements are consistent with a fully occupied framework and nearly fully occupied cation guest sites as found by microprobe analysis. Temperature dependent electrical resistivity and thermal conductivity have been measured from room temperature to 1200 K on a hot-pressed pellet. Electrical resistivity reveals metallic behavior. The negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity is between 22 and 25 mW/cm K. The sample shows n-type conductivity with a maximum figure of merit, zT of 0.3 at 1200 K. A single parabolic band model predicts a five-fold increase in zT at 800 K if carrier concentration is lowered. --more » Graphical abstract: The inorganic type-I clathrate phase with nominal composition Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} has been prepared by Al flux. Single crystal diffraction at 90 and 12 K reveal that the framework is fully occupied with the cation sites nearly fully occupied. The lattice thermal conductivity is low thereby suggesting further optimization of the carrier concentration will lead to a high zT. Display Omitted Highlights: {yields} Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} is a light element phase ideal for thermoelectric power generation. {yields} Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} is a high melting point cubic structure ideal for efficient power generation. {yields} The framework is fully occupied with the cation sites nearly fully occupied. {yields} Further optimization of the carrier concentration is expected to lead to a high zT.« less
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [1]
  1. Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, CA 95616 (United States)
  2. Materials Science, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
21494303
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 184; Journal Issue: 5; Other Information: DOI: 10.1016/j.jssc.2011.02.027; PII: S0022-4596(11)00095-8; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALUMINIUM; ALUMINIUM COMPOUNDS; BARIUM COMPOUNDS; CLATHRATES; CUBIC LATTICES; ELECTRIC CONDUCTIVITY; ELECTRON MICROPROBE ANALYSIS; MELTING POINTS; MONOCRYSTALS; SILICON COMPOUNDS; SPACE GROUPS; STRONTIUM COMPOUNDS; TEMPERATURE RANGE 0000-0013 K; TEMPERATURE RANGE 0065-0273 K; TEMPERATURE RANGE 0273-0400 K; TEMPERATURE RANGE 0400-1000 K; TEMPERATURE RANGE 1000-4000 K; THERMAL CONDUCTIVITY; THERMOELECTRIC PROPERTIES; X-RAY DIFFRACTION ALKALINE EARTH METAL COMPOUNDS; CHEMICAL ANALYSIS; COHERENT SCATTERING; CRYSTAL LATTICES; CRYSTAL STRUCTURE; CRYSTALS; DIFFRACTION; ELECTRICAL PROPERTIES; ELEMENTS; METALS; MICROANALYSIS; NONDESTRUCTIVE ANALYSIS; PHYSICAL PROPERTIES; SCATTERING; SYMMETRY GROUPS; TEMPERATURE RANGE; THERMODYNAMIC PROPERTIES; TRANSITION TEMPERATURE