A bulk polycrystalline sample of YBa 2 Cu 3 O 7−δ (δ ≈ 0.1) has been irradiated by γ-rays with 60 Co source. Non-monotonic behavior of T c (defined as the temperature at which normal resistance is halved) with increasing irradiation dose Φ (up to about 220 MR) is observed: T c decreases at low doses (Φ ≤ 50 MR) from initial value (≈ 93 K) by about 2 K and then rises, forming minimum. At highest doses (Φ ≥ 120 MR) T c goes down again. The temperature width, δT c , of 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-T c superconductor. The cross sections for the displacement of lattice atoms in YBCO by γ-rays due to the Compton process were calculated, and possible dpa values were estimated. The results obtained are discussed taking into account that sample studied is granular superconductor and, hence, the observed variations of superconducting properties should be connected primarily with the influence of γ-rays on intergrain Josephson coupling.
It is shown that the power‐like dependence of the mean dislocation velocity v̄ on load of v̄ ∼ ϱ H0/kT type can be obtained analytically via considering the dislocation motion through a two‐dimensional random array of point obstacles. This results from stochastic averaging over the motion parameters, even in the case when the load dependence for the probability of surmounting every distinct local obstacle is described by the usual exponential relation. The v̄ ∼ ϱ H0/kT relation and its stochastic interpretation are shown to account for the number of peculiarities in stress relaxation for copper in the temperature range 4.2 to 300 K.
An investigation is described of the kinetics of stress relaxation and poatrelaxational effects in normal (N) and superconducting (S) states of polycrystalline 99.9995% pure lead a t 4.2 OK. The work-hardening coefficient e(r) during stress relaxation has been found to be much larger than that Oact during dynamic deformation. It has also been revealed that Nr) depends on the state of the sample (N or S state) where eg) > Or' .Es wird die Kinetik der Spannungsrelaxation und der Nachwirkungseffekte in normal (N) and supraleitendem (S) Zustand von 99,9995yo-reinem, polykristallinem Blei bei 4,2 O K untersucht. Es wird gefunden, daB der Verfestigungskoeffizient O(*) wahrend der Spannungsrelaxation vie1 groBer a18 der Koeffieient Oact wahrend der dynamischen Verformung ist.Dariiber hinaus wird gefunden, daD fXr) vom Zustand der Probe (Noder S-Zustand) abhangt, wobei O$) > et).
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