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23 Na and 29 Si NMR Knight shifts in the silicon clathrate<mml:math xmlns:…

2000; American Physical Society; Volume: 63; Issue: 3 Linguagem: Inglês

10.1103/physrevb.63.033102

1095-3795

G. Ramachandran, Jianjun Dong, Otto F. Sankey, Paul F. McMillan,

High-pressure geophysics and materials

Large ${}^{23}\mathrm{Na}$ and ${}^{29}\mathrm{Si}$ Knight shifts are observed for the silicon clathrate ${\mathrm{Na}}_{16}{\mathrm{Cs}}_{8}{\mathrm{Si}}_{136}$ in magic angle spinning NMR experiments. Electrical conductivity measurements on cold-pressed samples of the material also indicate metallic behavior, with a room temperature value of $\ensuremath{\rho}$ $\ensuremath{\approx}41$ $\mathrm{m}\ensuremath{\Omega}\mathrm{cm}.$ An ab initio calculation of the s-projected density of states at the Fermi level leads to a simple interpretation of the distinct resonances observed for each of the three framework sites in ${}^{29\mathrm{Si}}$ NMR experiments.