Activation energies in superconducting high temperature ceramics

Low field a.c. susceptibilities of HgBa2Ca2Cu3O8+δ (Hg-1223) and Bi2Sr2CaCu2O8+δ (Bi-2212) have been studied. The loss peak of χ″, relevant to intergranular pinning, shifts to higher temperatures for increasing frequencies. The results can be fitted with an Arrhenius law, leading to activation energies Ea ≈ 1eV, but the hopping frequencies 0 are not realistic. More realistic values can be obtained by introducing a Fulcher law or a power law which is also characteristic of strongly interacting systems.