Surface morphology of PrBa2Cu3O7-δ single crystals after the long-lasting high-temperature reduction

The results of the detailed scanning electron microscopy study of PrBa₂Cu₃O_7-δ single crystals after the long-lasting high-temperature post-growth treatment are reported. The presence of the unstable decomposition products on the crystal surface indicates that the onset of superconductivity must be related to the structural transformations in the bulk (approximately 20% of the total volume of the examined crystals). The time-dependent character of the superconductivity in the Pr-123 crystals could be attributed to the migration of defects in the Pr−Ba sublattice from the bulk toward the surface.