The effect of electron irradiation with the energy of 2.5 MeV on the temperature dependences of the resistivity ρ(T) of an optimally doped YBa 2 Cu 3 O 7-δ single crystal has been studied. The temperature dependences of both fluctuation conductivity σ΄(T) and the pseudogap Δ * (T) on irradiation dose φ have been calculated within the local pair model. Here we show that with an increase in φ, the value of ρ(300 K) increases linearly, while T c decreases linearly. Concurrently, the value of ρ(100 K) increases nonlinearly, demonstrating a feature for φ 3 = 4.3•10 18 e/cm 2 , which is also observed in the number of other dose-dependent parameters. Regardless of the irradiation dose, in the temperature range from T c up to T 01 , σ΄(T) obeys the classical fluctuation theories of Aslamazov-Larkin (3D-AL) and Maki-Thompson (2D-MT), demonstrating 3D-2D crossover with increasing temperature. The crossover temperature Т 0 makes it possible to determine the coherence length along the с axis, ξ с (0), which increases by ~ 3 times under irradiation. Furthermore, the range of superconducting fluctuations above T c also noticeably increases. At φ 1 = 0, the dependence Δ * (T) typical for single crystals containing pronounced twin boundaries is observed with a maximum at T pair ~ 120 K and a distinct minimum at T = T 01 . It was determined for the first time that at φ 3 = 4.3•10 18 e/cm 2 the shape of Δ * (T) changes strongly and becomes the same as in optimally doped YBa 2 Cu 3 O 7-δ single crystals with a very low pseudogap opening temperature T * and noticeably reduced T pair , while at T c (φ) there are no singularities. With an increase in the irradiation dose up to φ 4 = 8.8•10 18 e/cm 2 , the shape of Δ * (T) is restored and becomes the same as in well-structured YBa 2 Cu 3 O 7-δ films and untwined single crystals. Moreover, in this case, T pair and Т * increase noticeably.
