X-Ray Absorption Study of the Local Structure At Potassium and Rubidium in K_3-xRb_xC₆₀

Abstract

Abstract X-ray absorption fine structure (EXAFS and XANES) studies of the K-edges of potassium and rubidium in K3C60, K2RbC60 and Rb3C60 reveal the local structure and site preferences of the alkali metals. Both K and Rb ions on tetrahedral interstices exhibit regular positions with respect to the C60 neighbours in agreement with crystallographic data, while for Rb ions located on octahedral interstices an off-center position is found. The K2RbC60 sample exhibits a clear preferential site occupation of the octahedral site by Rb, which is also reflected by the lattice constant, and indications for structural rearrangement of the Rb ions on octahedral sites around 50 K.