Phase separation and phase transitions inKC60: AC13NMR study

We present evidence from ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR for a low-temperature (LT) ${\mathrm{KC}}_{60}$ phase, similar to the one observed in ${\mathrm{RbC}}_{60}$, obtained by rapid quenching of a ${\mathrm{KC}}_{60}$ sample from high temperatures. The same sample exhibits phase separation of the high-temperature phase into ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{60}$. Distinct ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR spectra of the different phases and their temperature dependence are shown. High-resolution ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ magic angle spinning NMR experiments reveal a fraction of ${\mathit{sp}}^3$ carbon atoms in the LT phase, providing evidence for the proposed ‘‘polymerization’’ or ‘‘dimerization’’ of the ${\mathrm{C}}_{60}^{\mathrm{-}}$ molecules in the LT phase.