Structural and composition changes in superconducting ceramics locally irradiated by electrons

Abstract

The structural changes and the cation and anion compositions of the surface of superconducting YBa 2 Cu 3 O 7-x and Tl 2 Ba 2 CuO 6+x ceramics after local irradiation for several seconds by an electron probe with an accelerating voltage of 25 kV and a current exceeding 10 -7 A are investigated by secondary-electron emission and by cathodoluminescence and x-ray microanalysis in a scanning electron microscope. Morphologically altered regions are detected in the irradiation epicenter, where the structure, chemical composition, and phase composition of the original compound are completely lost. In the intermediate zone between the epicenter and the periphery a distribution of the secondary emission yield is observed with a complex character that differs for the yttrium and thallium ceramics, and anomalies appear in the cathodoluminescence spectra. The experimental data are interpreted on the basis of ideas of oxygen losses under the direct influence of the electron probe and related electronic processes in superconductors.

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

“…This result is indicative of the increase in the internal disorder because of irradiation promotes structural damages and weak-link breakage at the grain boundaries. On the other hand, the critical temperature, T c , has increased from 80 to 88 K; this result seems striking if we consider the results obtained in bulk [18] or YBCO single crystals [19,20] where T c is reported to change by order of 2 or 3 degrees. Other irradiation sources such as protons [21], fluorine [21] or helium ions [22] have been also employed to modify the transport properties of YBCO films.…”

“…Magnetization (M) measurements were conducted with the applied magnetic field H perpendicular to the film using a commercial magnetometer (Quantum Design PPMS) in a range of 0 to 10 000 Oe. Indirectly from these M-B loops the critical current density of the samples was determined using the Bean model [17,18]. The hysteresis loops M(B) were obtained after cooling the sample in zero field to the desired temperature of 5 K.…”