Superconducting fullerite Rb3C60 synthesized using alkali-metal azides as a source of the alkali metal showed time-dependent development of the superconducting phase based on electron spin resonance and low-field microwave absorption data. Time dependences of both signals observed for several hours after the synthesis were described by the Avrami diffusion model assuming the diffusion process Rb + C60 → Rb3C60. The model permits calculation of the Josephson penetration depth as λJ ≈ 1500Å, which was in agreement with other measurements.

A Model for Rubidium Diffusion in RbxC60 Fullerites. Stankowski, J., Kevan, L., Czyzak, B., Andrzejewski, B.: Journal of Physical Chemistry, 1993, 97[40], 10430-2