Experimental study of microstructure and critical current density of YBCO/Ag thick films under silver addition and electron irradiation

Abstract

Thick polycrystalline films of silver doped YBCO were produced by the standard screen printing method and irradiated with a source of electrons at 1000 kGy. The critical temperature , the zero resistance temperature , the broadening of the superconductor transition and normal resistance, measured at 298 K, changed substantially in the irradiated sample when compared to the non-irradiated specimen. A detailed study using Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) on the cross sectional surface of the films revealed that silver was distributed in small amounts at the grain boundaries while some regions showed silver-rich-like clumps on the surface. In both cases, silver was found in a metallic state only. Such distribution was also confirmed by SEM images. We found by x-ray diffraction analysis important microstructural changes on the irradiated sample. The critical current density showed a sixfold increase after the sample was irradiated. The enhancing is directly associated with the increase in the flux pinning generated by the irradiation induced defects.

Microstructural and chemical analysis performed by HRTEM and EDS on YBa2Cu3O7−x/Ag films irradiated with electrons

“…These defects, the majority, are as bend planes in between the planes in the unit cell are likely responsible for the enhancement of the density current in the material, as we have shown in previous work [20].…”

“…Wu et al [19] reported that the orientation of the fringes abruptly changes by an angle ≈12 • , which suggests formation of stacking faults similar to our situation. These defects are very important in the enhancement of some electrical properties of the superconductor material, especially on the J c as reported by Rangel et al [20].…”

“…They found an enhancement in J c attributed to the defects, which serve as effective pining centers. On the other hand, Rangel et al [20] succeeded increasing the J c in polycrystalline YBCO/Ag tick films when subject to electron irradiation at a dose of 1000 kGy. The increase in J c was from 3.9 × 10 5 to 2.6 × 10 6 A/cm 2 .…”

“…X-ray analysis [20] indicates that the irradiated samples present the 123/Ag (1 0 0) MgO (substrate) and minority phases such as BaCuO 2 and Y 2 BaCuO 5 . No traces of YBa 2 Cu 4 O (10−x) either YBa 2 Cu 4 O 8 (1 2 4) phases were found, indicating that the amounts encountered of such phases were so small that they did not yield reflecting plane signals on the analysis performed.…”

Tuning electric charge scattering in YBCO single crystals via irradiation with MeV electrons

“…For such crystals, the estimated energy losses for 1 MeV electrons amount to 3% to 8%. As revealed by electron microscopy, electron irradiation leads to the formation of point disorder and/or small clusters which act as pinning sites 40 .…”