Electron structure and temperature-dependent shifts in 133Cs NMR spectra of the Cs8Ge136 clathrate -: art. no. 115208

We have synthesized and characterized the type-II germanium clathrate Cs8Ge136. The cesium atoms are ordered in structure, occupying the larger hexakaidecahedra while the smaller dodecahedra are basically empty. Band structure and electrical resistivity data indicate that Cs8Ge136 is metallic. Temperature-dependent Cs-133 nuclear magnetic resonance measurements show a sharp, single peak at temperatures below 343 K and above 383 K. Between these two temperature limits, a broad second peak is also observed. The transition from one peak to two peaks is reversible upon a heating-cooling cycle and may be a result of a Cs-Cs dimer between two Cs atoms in adjacent germanium cages.