TEMPERATURE-DEPENDENCE OF LOCAL-STRUCTURE AROUND RB+ AND CS+ IONS IN ALKALI DOPED FULLERENES

Rb and Cs K-edge EXAFS spectra have been measured in the temperature r ange from 10 to 290 K, in order to investigate the temperature depende nce of local structure around Rb+ and Cs+ ions in various alkali doped fullerenes. It has been found that the alkali metal ions in Rb3C60, K RbC60 and Na2CsC60 occupy the center of the tetrahedral and octahedral sites of C-60 crystals. The metal ion in the octahedral site exhibits a large fluctuation in comparison with that in the tetrahedral site. The increase in sigma(2) of the t-site Rb-C for Rb3C60 has been observ ed around T-c, while the increase in sigma(2) has not clearly been obs erved for the o-site Rb-C in K2RbC60. The local structure around Rb+ i on in non-superconducting alkali doped fullerene Rb6C60 has also been studied to compare with that in superconducting fullerenes.