Distribution of K ions in intermediateKC60

Intermediate ${\mathrm{KC}}_{60}$ formed from the homogeneous ${\mathrm{KC}}_{60}$ phase at 400 K is investigated by differential scanning calorimetry, x-ray diffraction, dc resistivity, electron spin resonance (ESR), and magnetic ac susceptibility. We show that in intermediate ${\mathrm{KC}}_{60}$ the ${\mathrm{C}}_{60}$ sublattice is continuous over large distances but the K ions separate into small ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ and K-free ${\mathrm{C}}_{60}$ regions. ESR shows a large volume fraction of superconducting ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$. The ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ phase is finely distributed and the magnetic-field exclusion is small. ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ regions are compressed and K-free regions are expanded with respect to the corresponding bulk phases. The compression decreases the superconducting critical temperature (${\mathit{T}}_{\mathit{c}}$) from 19 to 16 K. The expansion of the K-free ${\mathrm{C}}_{60}$ regions decreases the orientational ordering transition temperature (at 260 K) by 10 K.