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Nd1+xBa2-xCu3Oy (Nd123ss) single crystals were isothermally grown under controlled oxygen partial pressure of 1% O2 at various growth temperatures (Tg) from 1000 to 1020 °C with a flux method. The flux composition of 20 mol% NdBa2Cu3Oy (Nd123) and 80 mol% Ba3Cu5O8 (035) was employed. Nd123ss single crystals grown at Tg≥1010 °C exhibited a transition temperature Tc≈95 K with transition width ≈1 K, the peak field (Bpk)≈2-3 T and the irreversibility field (Birr) at 77 K much higher than the experimental limit of 7 T. As the growth temperature is lowered, both the Bpk and Birr were reduced, which can be explained in terms of the chemical fluctuation which can occur at lower Tg.

Large Nd1+xBa2-xCu3Oy (Nd123ss) single crystal cubes of side 3 mm were fabricated isothermally by the flux method. The crystals exhibited a Tc of 95 K with a sharp superconducting transition. One crystal was cut into small pieces, and its magnetic properties were measured to study the spatial distribution of the superconducting properties. It was found that although Tc values were almost constant, a small but significant intrinsic difference in the Jc-B properties and irreversibility field was observed depending on the sample position. This suggests that the distribution of Nd-rich Nd123ss clusters are spatially different even within the same single crystal. Such differences may be caused by the time variation of Nd concentration in the liquid during crystal growth.

Superconducting transitions are measured in field-cooled cooling (FCC) and field-cooled warming (FCW) modes in external magnetic fields ranging between 1 mT and 7 T on various high-T c superconductors (single crystal and melt-processed YBa2-Cu3O7-δ, single crystals and melt-processed NdBa2Cu3O7-δ, and on various ternary 123-superconductors). Our measurements reveal that a two step transition is observed if the sample exhibits also the secondary peak effect in the magnetization loops.

The magnetization properties of a flux-grown (Nd123) single crystal were investigated by measuring DC magnetization hysteresis (M-H) loops in a wide temperature range (10-92 K) and for applied fields parallel and perpendicular to the c-axis of the sample. For both field directions, temperature-dependent fishtail peaks in the M-H loops are clearly observed at high temperatures above 70 K, and all the data could be scaled to a single master curve with the hysteresis loop width versus H plot when they are normalized with the peak field and its magnetization value , respectively. This indicates that the origins of the peak effect and the pinning are identical for this temperature range. We have also found that and the irreversibility field scale with the reduced temperature, (: critical temperature), and follow the relationship with a power n of 1.1-1.3. The anisotropy parameters of and of were deduced from the angular dependence of and at 88 K. We emphasize that all the present results support our proposal that the peak effect in the Nd123 originates from the localized Nd-Ba substituted regions with depressed .

Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LREs: La, Nd, Sm, Eu, Gd) form a solid solution . The presence of such solid solution caused a depression in the superconducting transition temperatures , particularly for La123, Nd123 and Sm123 when they are melt processed in air. Recently, we have found that the of these LRE123 superconductors can greatly be enhanced when they are melt processed in a reduced oxygen atmosphere. Furthermore, values of these superconductors were larger than that of a good quality Y123 superconductor in high magnetic fields at 77 K. In this article, on the basis of our study over the last several years, the melt processes for LRE - Ba - Cu - O are described, the microstructural and superconducting properties of the superconductors are reviewed and the flux pinning mechanism is also discussed.

Induced current densities and magnetic relaxation rates were measured over a wide temperature and field range on a single crystal and a melt processed sample of using a SQUID magnetometer. The temperature dependence of the magnetic relaxation rate shows a pronounced minimum at elevated temperatures. This leads to very high values of the effective pinning energy and for the single crystal and the melt processed sample respectively, for an applied magnetic field . Furthermore, these samples show a well developed fishtail effect, leading to a current density . This demonstrates that the fishtail effect is closely related to the low relaxation rates observed here.

YBCO MPMG samples, with 40% Y2BaCuO5, (Y-211) phase excess, were prepared using different thermal pretreatments during the temperature increase up to the partially melted state. No temperature gradient was applied during the slow-cooling growth process. Presintered samples turned out to be almost single grain, while all the others were characterized by the presence of a higher number of randomly oriented domains. Presintering favours compositional homogeneity, but, most important, enhances YBa2Cu3O7-x (Y-123) phase solidification kinetics. Though various samples show similar behaviours, concerning the values of magnetization critical-current densities (Jcm) measured at 77 K (Jcm approximately=104 A cm-2 with B//c, B=1 T), levitation forces are subject to noticeable variations related to granular macrostructures and reach a peak of over 2 kg, at 77 K, in the case of presintered material.

The effect of 10% BaSnO3 addition on the microstructure and the magnetic properties of MPMG-processed samples has been investigated. At high temperature, BaSnO3 was found to react rapidly with the liquid phases to form inclusions, a few micrometres in size, of a new phase containing Y, Ba, Cu, Sn, Pt, O components. It is difficult to homogeneously distribute these new phase inclusions in the microstructure, but the '123' grain size, the stoichiometry and the distribution of '211' inclusions do not seem to be affected by this doping. Moreover, in spite of these difficulties, we could locally show evidence of '211' refinement and the possibility of Tc enhancement. This results in sensible improvement in Jc(B) properties compared to undoped MPMG samples, up to 1.1*105 A cm-2 in zero field, at 77 K and 4*104 A cm-2 in 1 T.