Low-temperature transport properties of polycrystalline Ba 8 Ga 16 Sn 30

  • PDF / 103,027 Bytes
  • 4 Pages / 612 x 792 pts (letter) Page_size
  • 83 Downloads / 193 Views

DOWNLOAD

REPORT


J.L. Cohn Department of Physics, University of Miami, Coral Gables, Florida 33124

J.S. Dyck and C. Uher Department of Physics, University of Michigan, Ann Arbor, Michigan 48109

G.A. Lamberton, Jr. and T.M. Tritt Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634 (Received 17 June 2004; accepted 27 August 2004)

Low-temperature resistivity, Seebeck coefficient, thermal conductivity, and heat-capacity measurements were performed on Ba8Ga16Sn30. This compound crystallizes in a cubic type-VIII clathrate phase, space group I4¯3m, with the Ba atoms residing inside voids created by a tetrahedrally bonded network of Ga and Sn atoms. Ba8Ga16Sn30 exhibits semiconducting behavior above 150 K with a low thermal conductivity and thus may hold potential for thermoelectric applications.

I. INTRODUCTION

Semiconducting group-IV clathrates have recently been identified as showing potential for thermoelectric applications.1,2 Most of the work to date investigating the transport properties of clathrate compounds has focused on clathrates with the type I clathrate crystal structure (space group Pm3¯n). These compounds have the general formula A8ByC46−y, where atoms B (Al, Zn, Cd, Ga, In) and C (Si, Ge, Sn) are tetrahedrally bonded to make a framework that forms cages in which the guest atoms A (Na, K, Rb, Cs, Sr, Ba, Eu) reside. The encapsulated atoms are said to “rattle” inside their atomic-sized cages, thus creating strong phonon-scattering centers. The localized vibrations of these atoms are believed to cause a dramatic lowering in the lattice thermal conductivity. Provided the electrical conduction takes place mostly through the frame, the rattling guest atoms will not greatly diminish the electrical conductivity. Indeed, semiconducting Ge-based clathrates exhibit lattice thermal conductivities typical of amorphous materials while maintaining good electronic properties.3,4 Materials of this type were described by Slack1 as being “phononglass and electron-crystal” (PGEC) materials and meet one of the main criteria for finding new thermoelectric materials. As part of a comprehensive study to assess the lowtemperature transport properties of different clathrate

DOI: 10.1557/JMR.2004.0467 3556

http://journals.cambridge.org

J. Mater. Res., Vol. 19, No. 12, Dec 2004 Downloaded: 13 Mar 2015

compounds and their potential for thermoelectric applications, we have synthesized Ba8Ga16Sn30, a cubic material with the same general formula as that of type I clathrates but with a different crystal structure.5 In this report, we present low-temperature electrical and thermal transport measurements on Ba8Ga16Sn30 and evaluate its potential for thermoelectric applications. II. SAMPLE PREPARATION

Sample preparation consisted of mixing and reacting high-purity elements inside a pyrolitic boron nitride crucible, itself sealed inside a quartz ampoule, above the melting point of the constituents. The product was annealed for five days at 380 °C before removing from the furnace. The structural properties were ana

Data Loading...