NMR Studies on Orientational Ordering Phase Transition in Na_2CsC_<60>

概要

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Sodium-containing alkali metal fulleride, Na_2CsC_<60>, was studied by ^<13>C and ^<23>Na NMR below and above the face-centered cubic (fcc) to simple cubic (sc) phase transition temperature, T_m. It is shown that the C_<60> molecules rotate faster than the rotational correlation time of 1.6×10^<-5> sec above 〜140K and 2.4×10^<-9> sec around 300K. Using ^<23>Na NMR spectra broadened by the second-order quadrupole interaction, the electric field gradient at Na sites, e^2qQ/h, was estimated to be 940±20 kHz and less than 0.1 kHz below and above T_m, respectively. The detailed analysis suggests that Na atoms in sc phase have a covalent character with C_<60>molecules. It is also suggested that Na_2CsC_<60> is the first metallic plastic crystal.
社団法人日本物理学会の論文
1995-12-15