Effect of Non-Stoichiometry of High-Temperature Superconductors of the Composition Gd1 + xBa2 – yCu3O7 – δ on Vortex Pinning and on the Vortex Liquid–Glass Phase Transition

High-temperature superconducting film samples of the non-stoichiometric composition Gd1+xBa2–yCu3O7–δ have been systematically studied. The measured R(T) curves in magnetic fields have demonstrated a sharp change in the nature of pinning with the field, which indicates a possible phase transition of the pinned vortex system from a three-dimensional state to a quasi-two-dimensional one. The vortex structure pinning has been described within the thermally activated flux flow model. The analysis of the dependence of the vortex activation energy U0(B) on the magnetic field has indicated that the influence of thermal fluctuations on the vortex system in non-stoichiometric high-temperature superconductors Gd1+xBa2–yCu3O7–δ is smaller than that in stoichiometric superconductors of a similar composition.