Effect of ?-Irradiation on Superconductivity in Polycrystalline YBa2Cu3O7-?

A bulk polycrystalline sample of YBa2Cu3O7–δ (δ ≈︂ 0.1) has been irradiated by γ-rays with 60Co source. Non-monotonic behavior of Tc (defined as the temperature at which normal resistance is halved) with increasing irradiation dose Φ (up to about 220 MR) is observed: Tc decreases at low doses (Φ ≤ 50 MR) from the initial value (≈︂93 K) by about 2 K and then rises, forming a minimum. At highest doses (Φ ≤ 120 MR) Tc decreases again. The temperature width δTc of the resistive transition increases rather sharp with dose below 75 MR and somewhat drops at higher dose. We believe that this effect is revealed for the first time at γ-irradiation of high-Tc superconductors. The cross sections for the displacement of lattice atoms in YBCO by γ-rays due to the Compton process were calculated, and the possible displacements per atom (dpa) were estimated. The results obtained are discussed taking into account that the sample studied is a granular superconductor and, hence, the observed variations of superconducting properties should be connected primarily with the influence of γ-rays on intergrain Josephson coupling.