Composition variation and electron irradiation effects on the fluctuation conductivity in Y_1–zPr_zBa₂Cu₃O_7−δ single crystals

A comparative analysis of the changes in the fluctuation conductivity and characteristics of the superconducting state of YBa2Cu3O7–δ single crystals caused by various types of defects is carried out. These defects appeared due to irradiation with high-energy electrons (radiation doses from 1.4 to 8.8 1018 cm–2), changes in oxygen deficiency (0.08 ≤ δ ≤ 0.23) due to annealing at different temperatures, or doping with praseodymium (Y1–zPrzBa2Cu3O7−δ, 0 ≤ z ≤ 0.5 at optimal oxygen concentration). It is shown that the introduction of such defects leads to a significant expansion of the temperature range of the existence of excess conductivity, and upon doping with praseodymium, it also leads to the appearance of a thermally activated deflection on the temperature dependence of the electrical resistance. The effect of such defects on the superconducting transition temperature, Tc, and the coherence length along the c axis, ξc(0), is studied. In particular, ξc(0) more than quadruples (at z = 0.43), while the 2D-3D crossover point shifts towards higher temperatures. Possible reasons for the suppression of superconductivity in YBa2Cu3O7–δ upon irradiation with fast electrons and the qualitatively different temperature dependences of its resistivity in the basal plane, ρab (T), are discussed.