The temperature dependence of atomic displacements in superconducting K2RbC60 and non-superconducting Rb6C60 was studied by using X-ray powder diffraction methods. Rietveld refinement of the powder diffraction data for K2RbC60 at 10.2K revealed that the occupancy of Rb+ ions at an octahedral site was 71, rather than 100%. It was found that the atomic displacements of C atoms and metal ions in K2RbC60 exhibited an increase around the superconducting critical temperature. No such increase was observed in Rb6C60.

Y.Yoshida, Y.Kubozono, T.Urakawa, H.Maeda, S.Kashino, Y.Murakami, T.Ohta, F.Izumi, K.Yamada, Y.Furukawa: Solid State Communications, 1998, 105[9], 557-60