Structural and electronic properties of hydrogen-absorbed alkali-C60 compounds

The effect of hydrogen absorption on the structural and electronic properties of K3C60 superconductor was investigated by means of powder X-ray diffraction, magnetic susceptibility, and solid state NMR. No lattice expansion as well as no structural change were observed in powder X-ray diffraction by hydrogen absorption. Superconductivity was preserved and the superconducting transition temperature was not affected by hydrogen absorption. No distinct relationship was observed between the shielding fraction and the amount of absorbed hydrogen. Peak position and line shape of 13C NMR spectrum did not change by hydrogen absorption. Peak position of 1H NMR spectra suggested that hydrogen was almost neutral in the crystal. No significant difference was observed between K3C60 and hydrogeniabsorbed sample in 23Na NMR spectra. These facts suggest that absorbed hydrogen does not occupy octahedral or tetrahedral sites in the host f.c.c. lattice. Nuclear Curie-like behavior was observed in the temperature dependence of the 1H NMR intensity.