Rattler site selectivity and covalency effects in Type-I clathrates

Denis Arčon, Andrej Zorko, Peter Jeglič, Jingtao Xu, Jun Tang, Yoichi Tanabe, Satoshi Heguri, Katsumi Tanigaki

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


Type-I germanium clathrates comprised of Ga/Ge tetrakaidecahedra and dodecahedra cages that host alkaline earth atoms exemplify the properties of good thermoelectrics where the guest-atom anharmonic vibrations play a major role. However, while the host lattice-guest atom interaction is essential for this class of materials it is at the same time difficult to investigate due to the random Ga/Ge site occupation in the host lattice. In the present 71Ga NMR study of Sr8Ga16Ge30 and Ba8Ga16Ge30 samples we extract different Ga crystallographic site contributions from otherwise complex NMR spectra by exploring differences in their spin-lattice relaxation rates. Such approach opens a unique possibility for a site-selective study that directly proves non-negligible interaction of the anisotropic rattling motions of endohedral Sr with Ga atoms occupying the specific 24k sites of larger tetrakaidecahedral cages. This interaction affects electron-phonon coupling and modifies the local chemical environment-possibly even through weak covalent bonding of Sr to the cage. Our results are thus in agreement with claims that the conventional picture of purely ionic interactions between the rattling guest atoms and the cage is only approximate and that covalent effects should be taken into account in clathrates or similar thermoelectric cage materials.

Original languageEnglish
Article number014703
Journaljournal of the physical society of japan
Issue number1
Publication statusPublished - 2013 Jan


  • Nuclear magnetic resonance
  • Rattling
  • Thermoelectric

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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