“Glass-like” thermal conductivity gradually induced in thermoelectric Sr{sub 8}Ga{sub 16}Ge{sub 30} clathrate by off-centered guest atoms
- ICAMS, Ruhr-Universität Bochum, Bochum (Germany)
- Institut Laue-Langevin, 71 Avenue des Martyrs, CS 20156, Grenoble Cedex 9 (France)
The origin of the “glass-like” plateau in thermal conductivity of inorganic type I clathrates has been debated for more than a decade. Here, it is demonstrated that the low temperature thermal conductivity of Sr{sub 8}Ga{sub 16}Ge{sub 30} can be controlled by the synthesis method: A flux-grown sample has a “glass-like” plateau in thermal conductivity at low temperature, while a zone-melted sample instead has a crystalline peak. A combination of flux-growth and zone-melting produces an intermediate thermal conductivity. In a comprehensive study of three single crystal samples, it is shown by neutron diffraction that the transition from crystalline peak to “glass-like” plateau is related to an increase in Sr guest atom off-centering distance from 0.24 Å to 0.43 Å. By modifying ab initio calculated force constants for the guest atom to an isotropic model, we reproduce both measured heat capacity and inelastic neutron scattering data. The transition from peak to plateau in the thermal conductivity can be modeled by a combined increase of Rayleigh and disorder scattering. Measurement of heat capacity refutes simple models for tunneling of Sr between off-center sites. Furthermore, the electronic properties of the same samples are characterized by Hall carrier density, Seebeck coefficient, and resistivity. The present comprehensive analysis excludes tunneling and charge carrier scattering as dominant contributors to the “glass-like” plateau. The increased guest atom off-centering distance controlled by synthesis provides a possible microscopic mechanism for reducing the low temperature thermal conductivity of clathrates.
- OSTI ID:
- 22596968
- Journal Information:
- Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 18 Vol. 119; ISSN JAPIAU; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ATOMS
CARRIER DENSITY
CHARGE CARRIERS
CLATHRATES
GALLIUM COMPOUNDS
GLASS
INELASTIC SCATTERING
MONOCRYSTALS
NEUTRON DIFFRACTION
NEUTRON REACTIONS
NEUTRONS
PEAKS
SPECIFIC HEAT
STRONTIUM COMPOUNDS
SYNTHESIS
TEMPERATURE RANGE 0065-0273 K
THERMAL CONDUCTIVITY
TUNNEL EFFECT
ZONE MELTING