EFFECT OF GAMMA-IRRADIATION AND SILVER DOPING ON YBCO SUPERCONDUCTOR

The effect of gamma-irradiation and silver doping on the properties of YBCO superconductors has been studied by electrical resistance measurements and x-ray diffraction techniques. The zero-resistance superconducting transition temperature of (YBCO)(1-x)Ag-x systematically increase by about 2 K with an increase of Ag content up to x = 0.04. Further increase in Ag content decreases the transition temperature. The normal-state resistance decreases up to a factor of 3.4 with an increase of Ag content. No significant change in the transition width has been observed due to silver addition up to x = 0.30. Undoped YBCO and the Ag-doped specimens of (YBCO)(1.96)Ag-0.04 were irradiated with gamma-rays up to an integrated gamma-dose of 77 MR. The normal-state resistance of the specimens gradually increases and the transition temperature slightly decreases with increase of gamma-dose. The intensities of the x-ray diffraction peaks of the monolayers of the sample powders decrease with gamma-irradiation without noticeable change of diffraction angles or peak widths. These observations indicate that the high-T-c supconductor YBCO is quite sensitive to gamma-irradiation but drastic lattice expansion does not occur up to a gamma-dose of 77 MR

Voltage-current characteristics of polycrystalline (Bi,Pb)(2)Sr2Ca2Cu3O10 superconductor at different magnetic fields and temperatures

The voltage-current characteristics of polycrystalline (Bi,Pb)(2)Sr2Ca2Cu3O10 superconductor were investigated at temperatures from 80 to 105 K under magnetic field up to 0.4 T. In magnetic field considerable broadening in the transition width occurs which depends on the processing conditions and microstructure of the sample. I-V data below T-c were fitted to a power law expression V similar to I-beta to obtain beta. We have found that beta decreases rather rapidly with increase of magnetic field and temperature, in low magnetic fields and at temperatures quite below T-c, respectively. Similar behavior was observed for the variation of the critical current as a function of temperature and magnetic field. The beta values are found to change linearly as a function of critical current at relatively law values of I-c

EFFECT OF GAMMA-IRRADIATION ON PURE AND SILVER-DOPED YBCO SUPERCONDUCTOR

Specimens of high-T(c) superconductors, YBCO and (YBCO)1.96 Ag0.04, were irradiated with gamma-rays up to an integrated dose of 77 MR. Electrical resistance vs temperature and the X-ray diffraction patterns of the monolayers of the sample powders were obtained before and after the irradiations. The normal state resistance of the pure and Ag-doped YBCO specimens gradually increase as the gamma-dose increases. The intensities of the X-ray diffraction peaks of the monolayers of the YBCO powders decrease with gamma-irradiation without significant change of diffraction angles or peak widths. The zero resistance transition temperature of the Ag-doped YBCO specimens decreases by about 0.5% with gamma-irradiation at 77 MR. These observations indicate that the high-T(c) superconductor YBCO is quite sensitive to gamma-irradiation but drastic lattice expansion does not occur up to a gamma-dose of 77 MR

Effect of gamma irradiation on structure and electrical properties of (Bi,Pb)(2)Sr2Ca2Cu3O10 superconductor

Specimens of pure and Pb-doped high-T-c superconductors Bi2Sr2Ca2Cu3O10 (BSCCO) were irradiated with gamma-rays up to an integrated dose of about 225 MR. The variations of normal state resistance, transition temperature, critical current and lattice parameters with gamma-irradiation were studied. The normal state resistance increases with increase of gamma-dose at zero applied magnetic field, whereas the transition temperature and the critical current decrease with the same gamma-dose. The intensities of the X-ray diffraction peaks of the pure samples decrease with increase of gamma-dose without significant change of diffraction angles or peak widths. BSCCO superconductor is found to be quite sensitive to gamma irradiation but drastic lattice expansion do not occur up to 225 MR. (C) 1997 Academic Press Limited

Effect of magnetic field and temperature on the voltage-current characteristics of YBCO superconductor

Voltage-current characteristics of YBCO superconductor was studied under magnetic field up to 0.4 T at different temperatures below T-c. The critical temperature decreases and the transition width broadens under magnetic field. V-I data below T-c were fitted to a power law expression V similar to I-beta(T,I-B) in which beta(T,B) is found to decrease with increase of magnetic field and temperature, gradually approaching unity as T approaches T-c, being independent of magnetic field. Similarly beta(T,B) approaches unity as magnetic field increases being independent of temperature

Dissipative behavior and gamma-irradiation of silver-sheathed Bi1.8Pb0.4Sr2Ca2Cu3Ox tape

Dissipative mechanisms in Bi1.8Pb0.4Sr2Ca2Cu3Ox tapes were investigated using magnetoresistance measurements and V-I characteristics. A considerable broadening of the resistive transition in applied magnetic field was observed up to a field of 0.5 T. The temperature and magnetic field dependence of the resistance R(T,B) were fitted to the Arrhenius relation and from which the magnetic field dependence of the pinning energy U-0(B) similar to B-alpha with alpha approximate to 0.9 was derived. The variations of the critical current densities J(c) with temperature and magnetic field before and after gamma-irradiation were also studied. The temperature dependence of J(c)(T) was fitted to the relation J(c)(T) similar to (1 - T/T-c)(n) with n = 1.9 and discussed in terms of thermally activated flux flow (TAFF). However, J(c)(B) results were explained based on the weak links, grain boundaries, and Josephson junctions in which it shows a power law behaviour J(c)(B) similar to B-0.5. At relatively low temperatures and magnetic fields, the critical current density was increased with a gamma-irradiation up to a dose of 100 MR