The Dynamics of the Guests in Filled Germanium Clathrates

Author

Raphäel P. Hermann
Fernande Grandjean, Missouri University of Science and TechnologyFollow
Veerle M. Keppens
Werner Schweika
George S. Nolas
David G. Mandrus
Brian C. Sales
Hans Martin Christen
Pierre Bonville
Gary J. Long, Missouri University of Science and TechnologyFollow

Abstract

In the filled gallium-germanium clathrates, R₈Ga₁₆Ge₃₀, where R is Ba, Sr, or Eu, the guests are located in two large cages and are weakly bound to the crystalline clathrate framework. The caged guests exhibit a localized "rattling" vibrational mode that provides an efficient mechanism for reducing the thermal conductivity. Inelastic neutron scattering and nuclear inelastic scattering measurements have yielded the phonon density of states in R₈Ga₁₆Ge₃₀', the line width of the localized vibrational modes is found to be an important parameter in determining the lattice thermal conductivity. Neutron diffraction studies on R₈Ga₁₆Ge₃₀ have shown that the guests in the larger cage are located off-center, and it was proposed that their jumping about the four off-center locations is responsible for the observed glass-like thermal conductivity at temperatures below 10 K. The detection of such slow guest motion is challenging because the typical time and energy scales involved are ca. 4 ns and 1 µeV, respectively. We have studied the slow europium tunneling dynamics in Eu₄Sr₄Ga₁₆Ge₃₀ by both Mössbauer and microwave absorption spectroscopy.

Recommended Citation

R. P. Hermann and F. Grandjean and V. M. Keppens and W. Schweika and G. S. Nolas and D. G. Mandrus and B. C. Sales and H. M. Christen and P. Bonville and G. J. Long, "The Dynamics of the Guests in Filled Germanium Clathrates," Proceedings of the Materials Research Society Symposium (2005, Boston, MA), vol. 886, pp. 389 - 394, Materials Research Society (MRS), Jan 2006.

Meeting Name

2005 Materials Research Society Fall Meeting (2005: Nov. 28-Dec. 1, Boston, MA)

Department(s)

Chemistry

Keywords and Phrases

Crystalline Clathrates; Europium Tunneling Dynamics; Inelastic Neutron Scattering; Inelastic Scattering; Microwave Absorption Spectroscopy; Absorption Spectroscopy; Crystalline Materials; Elasticity; Neutron Scattering; Parameter Estimation; Phonons; Thermal Conductivity; Thermal Effects; Vibration Control; Zeolites; Semiconducting Germanium

International Standard Book Number (ISBN)

978-1558998407

International Standard Serial Number (ISSN)

0272-9172

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2006 Materials Research Society (MRS), All rights reserved.

Publication Date

01 Jan 2006