X-RAY-ABSORPTION STUDY OF THE LOCAL-STRUCTURE AT POTASSIUM AND RUBIDIUM IN K3-XRBXC60

X-ray absorption fine structure (EXAFS and XANES) studies of the K-edg es of potassium and rubidium in K3C60, K2RbC60 and Rb3C60 reveal the l ocal structure and sire preferences of the alkali metals. Both K and R b ions on tetrahedral interstices exhibit regular positions with respe ct to the C-60 neighbours in agreement with crystallographic data, whi le for Rb ions located on octahedral interstices on off-center positio n is found. The K2RbC60 sample exhibits a clear preferential site occu pation of the octahedral site by Rb, which is also reflected by the la ttice constant, and indications for structural rearrangement of the Rb ions on octahedral sites around 50 K.