The Dynamics of the Guests in Filled Germanium Clathrates
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.
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.
2005 Materials Research Society Fall Meeting (2005: Nov. 28-Dec. 1, Boston, MA)
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
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01 Jan 2006