Low temperature phase transition in superconducting ceramics YBa2Cu3O7

Temperature dependence of the narrow band cathode luminescence intensity from superconducting (SC) ceramics YBa2Cu3O7 present wide asymmetric hysteresis covering from Tl=30 K to Tc=98 K. Hysteresis is displayed only in the case when the sample is cooled to lower than Tl=30 K. Temperature variation rates influence the lower and upper hysteresis branches in different ways. The results are accounted for in the framework of representation of the first-order phase transition (PT) between two SC phases. The assumption is made as to kinetic blocking of the metastable phase nucleus in the range of 30-98 K and stability loss of the high temperature SC phase at 30 K