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Abstract
In this study, the change of superconducting and normal characteristics was studied in (77-290)K temperature range by means of determining the resistivity of the polycrystalline YBa2Cu3Ox sample stored in room conditions for 30 years after a short-term heat treatment at 400°C and slowly freezing. It has been shown that in this case, the heat treatment does not affect the width of the superconducting transition of the sample, but results in a significant increase in its resistivity in the fluctuating region and a slight reduction in the critical Tc temperature of the superconducting transition. It has been found out that both before and after the heat treatment a temperature T*>> Tc is observed in the sample below which the pseudogap mode is established characterized by a faster reduction than the linear resistivity. Moreover, if the Tc is reduced by only one degree after the heat treatment, then the T* decreases by 26.5K, i.e. the narrowing of pseudogap mode temperature range and, hence, the extension of metal behavior temperature range is observed. In addition, the resistivity and its temperature slope are substantially reduced in comparison with the initial one from 110K to room temperature. These results are qualitatively interpreted within the frames of the redistribution model of defects previously available in the Cu-O chains and planes as well as new structural ones of the spatial lattice of the sample caused by the heat treatment.
