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We report on the microwave surface resistance of melt-textured Y_1.6Ba_2.3Cu_3.3O_7-x samples, doped with different amount of B_2O_3 and, subsequently, irradiated by thermal neutrons at the fluence of 1.476 \times 10^17 cm^-2. The microwave surface resistance has been measured as a function of temperature and DC magnetic field. The experimental results are quantitatively discussed in the framework of the Coffey and Clem theory, properly adapted to take into account the d-wave nature of cuprate superconductors. By fitting the experimental data at zero DC field, we have highlighted the effects of the induced defects in the general properties of the samples, including the intergranular region. The analysis of the results obtained at high DC fields allowed us to investigate the fluxon dynamics and deduce the depinning frequency; in particular, we have shown that the addition of B_2O_3 up to 0.1 wt% increases the effectiveness of the defects to hinder the fluxon motion induced by the microwave current., Comment: 9 pages, 8 embedded figures, accepted for publication in Physica C

In the present work, we have investigated the effect of neutron irradiation on the pinning and transport properties of melt-textured SmBaCuO samples. It was observed that the critical current density is strongly enhanced at various temperatures and magnetic fields up to 5 T. The enhancement is larger at low temperatures compared to high temperatures. This difference is discussed in terms of the defect structure. Our investigations on YBCO superconductors also show a similar behavior. But the critical current density enhancement with neutron irradiation is smaller in this system compared to SmBaCuO system. Possible reasons for this difference are also discussed. (C) 2004 Elsevier B.V. All rights reserved.

Synthesis in the ammonium nitrate melt was used to obtain polycrystalline samples of complex copper-ruthenium oxides RuSr(2)Ln(1+x)Ce(1-x)Cu(2)O(10-y) (Ru-1222) and RuSr(2)LnCu(2)O(8) (Ru-1212) (Ln = Sm, Gd and Eu), as well as Ru(1-x)A(x)Sr(2)GdCu(2)O(8) (A = Pd, Os, Rh; x = 0.2, 0.4). Magnetic and superconducting properties of these samples were studied. The superconducting transition temperature in the RuSr(2)Ln(1.5)Ce(0.5)Cu(2)O(10-y) compound was found to be higher compared with the samples obtained using the solid state synthesis. At the same time, the new synthesis process has a much shorter duration. RuSr2GdCu2O8 compound is also produced faster in the ammonium nitrate melt. Doping with Os, Rh, Pd expedites the development of superconductivity in these samples. (C) 2002 Elsevier Science B.V. All rights reserved.

Penetration of AC field in BSCCO-2212 single crystals was studied using the magneto-optic technique. Profiles of the field amplitude were measured across the sample. The profile shape was found to change essentially with the field frequency. At lower frequencies the profiles have a dome-like shape characteristic of the geometrical barrier, whereas at higher frequencies the profiles acquire a typical Bean-like shape manifesting the flux pinning. Measurements at higher frequencies have shown that pinning is effective in the whole temperature range up to T C . This shows that the position of the depinning line, which is commonly supposed to lie well below T C even in zero field, has to be corrected to take into account the giant flux creep in BSCCO.