Civale, L., H. Pastoriza, F. de la Cruz, J. Guimpel, G. Nieva, J. M. Heintz, O. Durmeyer, and J. P. Kappler. "Meissner fraction of insulating samples of oxide superconductors." Solid State Communications 72, no. 4 (1989): 341–344.
Abstract: The tendency towards superconducting granularity with sample degradation is a common feature of oxide superconductors. We present magnetic, transport and calorimetric results in LiTi$2Ο4$ which show that the topological tendency to segregate the superconducting state into islands surrounded by thin insulating layers is related to the structure of the material rather than to a mechanism associated to high T$_C$. We emphasize that insulating samples with small Meissner fraction can have a superconducting volume fraction close to unity.