Structure degradation and conductivity variation in the perovskite phase of yttrium-barium ceramics

It is found that the perovskite phase of yttrium-barium ceramics with the composition [(Y,Ba)CuO3−Δ/3]3 under normal conditions is metastable and exhibits atmospheric degradation with time. This degradation results in the formation of an orthorhombic YBa2Cu3O7−δ phase characterized by the superconducting transition at T c =91 K. As a result of the degradation, the conductivity type changes from mixed metallic-semiconductor (ρ(T) = const) to purely metallic in the temperature interval from 100 to 300 K.