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

Abstract

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.

Electron irradiation effects in doped high temperature superconductors YBa2Cu3−x MxOy (M = Fe, Ni; x=0; x=0:01)

“…The results of these irradiation experiments * E-mail: grant@yerphi.am have been documented in the scientific literature as follows: ions [1,2], γ-quanta [3,4], protons [5,6], neutrons [7,8], electrons [1,[8][9][10][11][12] The aim of these experiments is to determine the influence of atomic disordering on the order parameter of HTSC; revealing the symmetry of this parameter is an important step towards understanding the mechanism behind HTSCs [13,14]. Experiments have shown that irradiation by ions, neutrons and protons causes point and cluster type structural defects in all the sub-lattices of a HTSC, while irradiation with γ-quanta causes mainly point defects in the oxygen sub-lattice of HTSC.…”

“…The obtained values of δT = 1÷2.5 K coincide with those previously determined for both polycrystalline [4,19] and pure single crystalline HTSC. Note, that T is defined by the transition from granules into superconductivity and is an intrinsic property of the HTSC sample, conversely, T J which is determined by intergranular properties, is more sensitive to the irradiation of the sample [2,9].…”

“…A comparison of the initial parameters of "pure" HTSC samples used in these experiments with those documented in current literature demonstrates that both the ceramic and single crystal materials used were of sufficient uniformity [12,20]; furthermore, the oxygen content of the samples was shown to be optimal with ∼ = 6 9 [4,18]. The obtained values of δT = 1÷2.5 K coincide with those previously determined for both polycrystalline [4,19] and pure single crystalline HTSC.…”

“…The weak bonds are formed on the boundaries of granules containing a large number of non-uniformly distributed structural defects [6,18]. The intergranular layer is often dielectric in nature [4,18].…”

Studies on the Gamma Radiation Responses of High Tc Superconductors

“…These contradictions have not been completely explained yet; some authors even attribute these behaviors to a "sample effect" (Polyak et al, 1990). However, Belevtsev et al (Belevtsev et al, 2000) has determined the relationship between the superconducting order parameter 2 and the density of oxygen vacancy rate lower bound, expressed in displacement per atom, in order to achieve significant modification of the superconducting behavior. On this ground, by means of the Oen-Holmes-Cahn atom displacement calculation algorithm (Oen & Holmes, 1959;Cahn, 1959), they calculated the incoming gamma quanta total flux inducing a dpa rate of about 0.02.…”