Distribution of K ions in intermediate KC60

G Faigel, G Bortel, M Tegze, László Gránásy1,2, S Pekker, G Oszlányi, O Chauvet, G Baumgartner, L Forró, Stephens P, G Mihaly, A Jánossy

1Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, P.O. Box 49, Budapest H-1525, Hungary
2BCAST, Brunel University, Uxbridge, Middlesex, UB8 3PH, United Kingdom

Intermediate KC60 formed from the homogeneous KC60 phase at 400
K is investigated by differential scanning calorimetry, x-ray
diffraction, de resistivity, electron-spin resonance (ESR), and
magnetic ac susceptibility. We show that in intermediate KC60
the C-60 sublattice is continuous over large distances but the K
ions separate into small K3C60 and K-free C-60 regions. ESR
shows a large volume fraction of superconducting K3C60 The K3C60
phase is finely distributed and the magnetic-field exclusion is
small. K3C60 regions are compressed and K-free regions are
expanded with-respect to the corresponding bulk phases. The
compression decreases the superconducting critical temperature
(T-c) from 19 to 16 K. The expansion of the K-free C-60 regions
decreases the orientational ordering transition temperature (at
260 K) by 10 K.