AN EXAFS STUDY ON THE LOCAL-STRUCTURE IN THE NA2CSC60 SUPERCONDUCTOR

Cs K-edge extended X-ray absorption fine structure (EXAFS) spectra of Na2CsC60 are measured in order to determine the local structure around the Cs+ ion. The structural change accompanied by the order-disorder phase transition at 299 K is investigated in detail on the basis of th e EXAFS spectra at 20, 295 and 317 K. It has been confirmed that Na2Cs C60 takes a face-centered-cubic structure at 317 K, while it takes a s imple-cubic structure at 20 and 295 K. It has also been found that the Cs+ ion at the octahedral site is not located out-of-center of the oc tahedral site but is located on the center.