Aging of the superconducting properties of thin Y1Ba2Cu3Ox films and their passivation by an amorphous YBaCuO layer

The values of the critical temperature Tc, the superconducting transition width ΔT, the critical current density Jc, and the resistivity at room temperature of thin laser ablated Y1Ba2Cu3Ox films were examined for a period of more than eight months. One set of samples showed the aging of films produced on different substrate materials. Films on SrTiO3 (100) substrates reached a stable state after three months. Surprisingly we found an increased Jc in time for a film produced on ZrO2 (100). In contrast films on random oriented ZrO2 single crystals showed the strongest degradation. For that reason this substrate material was chosen for a second set of samples, which we used to study the influence of an amorphous YBaCuO passivation layer. We found that the ''in-situ'' passivation is able to prevent the thin Y1Ba2Cu3Ox film from degrading. For such a film no change in Tc and in the sharpness of the superconducting transition was observed. The only aging effect we found was a slight change in room temperature resistivity. In contrast an ''ex-situ'' passivated film more closely resembles the unpassivated film. For that reason we conclude that even a short contact with moisture leads to a degradation of the Y1Ba2Cu3O7 thin films. (orig.)