Origin of peak effect in the magnetization hysteresis loop of melt-processed REBa2Cu3Oy superconductors
TL;DR: In this paper, the origin of the peak effect exhibited in the magnetization hysteresis loops of light RE-123 samples in intermediate fields at 77 K was investigated by transmission electron microscope (TEM) and superconducting quantum interference device magnetometer, to explain the source of peak effect.
Abstract: Melt-processed Sm-123 samples with an excess Sm2BaCuOy (Sm-211) phase is studied by transmission electron microscope (TEM) and superconducting quantum interference device magnetometer, to explain the origin of the peak effect exhibited in the magnetization hysteresis loops of light RE-123 samples in intermediate fields at 77 K. TEM images of the sample showing peak effect reveal dilute concentrations of areas with ortho-II structure distributed on a nanometer scale within the twin regions of the sample. The ortho-II structure is an oxygen deficient 123 with a lower Tc than the bulk of the material and will be a source of flux pinning by turning normal in high fields, thus contributing to the peak effect. With an increase in Sm-211 concentration, the peak effect disappears from the hysteresis loop, as does the ortho-II structure in the TEM images.
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TL;DR: In this article, a binary (Nd, Sm)-Ba-Cu-O superconductors with Tc of 96 K and a high irreversibility field up to 8 T have been fabricated in air via a newly developed technique.
Abstract: Binary (Nd, Sm)-Ba-Cu-O superconductors with Tc of 96 K and a high irreversibility field up to 8 T have been fabricated in air via a newly developed technique. The initial composition was controlled by using binary (Nd, Sm)2BaO4 as an addition. In comparison with both NdBaCuO and YBaCuO melt-textured superconductors, the present composition showed a remarkable enhancement of critical current densities in an intermediate field regime (1-3 T). Microstructural observations and compositional analysis showed that the distributions of Nd and Sm in the (Nd, Sm)-123 matrix were homogeneous while the atomic ratio between these two rare earth elements was inconsistent with that in the nominal composition. These new characteristics were thought to cohere with the different solubilities between Nd and Sm in the liquid phase. Finally, trapped magnetic field mapping showed a single-domain shape of the trapped field, which indicated the growth of a single grain in the samples.
26 citations
TL;DR: In this paper, a very uniform distribution of nearly spherical Nd-422 inclusions with 80% of the particles having a diameter less than 1 μm, in the highly textured NdBa 2 Cu 3 O 7-δ (Nd-123) superconductor was obtained.
Abstract: NdBa 2 Cu 3 O 7-δ (Nd-123) superconductor has been processed to obtain a highly textured microstructure with micrometer-sized spherical Nd 4 Ba 2 Cu 2 O 10 (Nd-422) inclusions through a process that involves the infiltration of liquid phases into a shaped preform followed by its slow cooling through the peritectic formation temperature of Nd-123. The process was carried out in high-purity argon (maximum of 4 ppm of oxygen) to reduce the formation of low-T c solid solutions. A major advantage of the process is that it minimizes the possibility of Nd-422 coarsening in the liquid. The result is a very uniform distribution of nearly spherical Nd-422 inclusions with 80% of the particles having a diameter less than 1 μm, in the highly textured Nd-123 matrix. Since the present process eliminates shrinkage and large hollows within the interior of the samples, it can enable the fabrication of 3-dimensional complex-shaped objects with good dimensional tolerance and high J c for applications. The critical current densities in the Nd-123/Nd-422 composites have been measured and the values obtained are discussed in the context of the microstructure of the material.
25 citations
TL;DR: In this article, it was shown that when high p O 2 treatments are properly chosen, Nd123/422 interfaces become the dominant flux pinning center, strongly increasing the critical currents at low and intermediate magnetic fields.
Abstract: A competing effect inducing both an enhancement of interface pinning and aging of the critical currents has been established in NdBa 2 Cu 3 O 7− δ /Nd 4 Ba 2 Cu 2 O 10 (Nd123/422) melt-textured ceramic composites upon high oxygen pressure annealing. We demonstrate that, when high p O 2 treatments are properly chosen, Nd123/422 interfaces become the dominant flux pinning centre, strongly increasing the critical currents at low and intermediate magnetic fields. It is suggested that Nd123/422 interfaces are enriched in antisite defects, which are properly oxygenated only upon high p O 2 annealing. Additional evidence for the enhanced oxygenation is gained from the observation of a consequent decrease of the field induced anomaly at intermediate fields. A second consequence of high pressure oxygenation is the appearance of an aging effect in the critical currents and irreversibility line. This is the first time that aging is described in Nd123/422 ceramic composites.
7 citations
TL;DR: In this article, the authors investigated the upper solubility limit of Nd123ss in industrial argon and critically reviewed these flux pinning mechanisms on the basis of a phase transformation theory.
Abstract: Unlike YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (Y123) which is a line compound for the cations, the Nd-Ba-Cu-O superconductor forms a solid solution Nd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 7-/spl delta// (Nd123ss) between Nd and Ba. The presence of such a solid solution tends to cause a depression of the superconducting transition temperature (T/sub c/) and a broad transition. Processing in a low oxygen partial pressure (Po/sub 2/) can produce a high T/sub c/ and enhanced critical current density (J/sub c/). However, there are controversies on flux pinning mechanisms for this material, In this paper, we investigated the upper solubility limit of Nd123ss in industrial argon and critically reviewed these flux pinning mechanisms on the basis of a phase transformation theory. We believe that precipitation mechanism based on the change of the solubility limits of Nd123ss with Po/sub 2/ offers a consistent explanation to the enhanced flux pinning in the system. This may provide guidelines for further improvement in superconducting properties of bulk 123 materials.
3 citations
TL;DR: In this article, a competing effect inducing both an enhancement of interface pinning and aging of critical currents has been established in NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta/Nd/sub 4/Ba/simulated 2/cu/sub 1/O 2/O 10/sub 10/ (Nd123/422) melt-textured ceramic composites upon high oxygen pressure annealing.
Abstract: A competing effect inducing both an enhancement of interface pinning and aging of the critical currents has been established in NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///Nd/sub 4/Ba/sub 2/Cu/sub 2/O/sub 10/ (Nd123/422) melt-textured ceramic composites upon high oxygen pressure annealing. It is suggested that Nd123/422 interfaces are enriched in antisite defects, which are properly oxygenated only upon high PO/sub 2/ annealing. Additional evidence for the enhanced oxygenation is gained from the observation of a consequent decrease of the field induced anomaly at intermediate fields.
1 citations
References
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TL;DR: The anomalous magnetization characteristic, intra-grain granularity and the magnitude of the flux pinning in single crystals of YBa2Cu307-δ are intimately linked as mentioned in this paper.
Abstract: The anomalous magnetization characteristic, intra-grain granularity and the magnitude of the flux pinning in single crystals of YBa2Cu307–δ are shown to be intimately linked. As the nominal oxygen deficiency δ decreases towards zero, the flux pinning declines and the crystals lose their explicitly granular signature. As δ is seldom specifically controlled at levels below ˜0.05 in even the most carefully made materials, small oxygen deficiencies may contribute significantly to both the flux pinning and the weak-link properties.
620 citations
TL;DR: In this paper, the authors showed that rare earth (RE) ions with large radii exhibit relatively low T c due to the presence of RE-Ba solid solution and that this solid solution can be suppressed if these superconductors are melt processed in a reduced oxygen atmosphere.
Abstract: REBa2Cu3Oy superconductors with rare earth (RE) ions with large radii (RE: La, Nd, Sm) exhibit relatively low T c due to the presence of RE-Ba solid solution. We have found that this solid solution can be suppressed if these superconductors are melt processed in a reduced oxygen atmosphere. We have also found that critical current densities of these superconductors are higher than those of melt processed YBa2Cu3Oy with fine Y2BaCuO5 inclusions in a high field region. The irreversibility line was also shifted toward the higher H-T region. We believe that flux pinning in these superconductors is ascribable to a finely distributed RE(Ba1-x , REx )2Cu3Oy phase in a good superconductive matrix.
301 citations
TL;DR: In this paper, a theoretical estimation of the contribution of 211 precipitates to flux pinning is also presented, and a value of pinning energy, U, comparable to that of conventional superconductors is obtained.
279 citations
TL;DR: In this paper, the authors report on the ordered oxygen structures and superconducting properties of YBa2Cu3Ox samples prepared in precisely controlled oxygen environments using a solid-state ionic technique.
Abstract: A PLOT of the superconducting transition temperature (Tc) against oxygen content (x) for YBa2Cu3Ox exhibits two 'plateaus' when oxygen is removed from the material at low temperatures. Tc remains nearly constant at ∼60K for x= 6.6–6.7 and nearly constant at ∼90 K for x= 6.8–7.0. It is now common to assume that there are two distinct superconducting phases in YBa2Cu3Ox, the '60-K' and '90-K' phases, and that the two plateaus correspond to single-phase regions of the respective phases1,2. YBa2Cu3Ox samples prepared at low temperatures contain a variety of ordered oxygen superstructures3–5. Several theoretical studies have tried to predict the phase equilibria between these ordered structures6,7 and to explain how oxygen ordering leads to the Tc plateaus8,9, but no clear understanding of the interrelationships amongst these factors has yet emerged. This is partly because the techniques used previously to prepare the low-temperature samples do not control or monitor all of the key processing variables, particularly the oxygen partial pressure. Here we report on the ordered oxygen structures and superconducting properties of YBa2Cu3Ox samples prepared in precisely controlled oxygen environments using a solid-state ionic technique. We find no evidence for phase separ-ation between structures that have widely different oxygen content, but we do see electron diffraction evidence for phase separation between distinct phases that differ only slightly in oxygen content, and these regions of phase separation coincide with the Tc plateaus. These results show that the commonly held view that the two plateaus correspond to single-phase regions of respective 60-K and 90-K phases is incorrect: the changes in superconducting properties with oxygen content in YBa2Cu3Ox cannot be explained on this basis.
232 citations
TL;DR: In this paper, the magnetization behavior of quench and melt growth (QMG)-processed YBa2Cu3O7 can be understood in terms of the critical state model.
Abstract: Magnetization measurements have been conducted on YBa2Cu3O7 samples fabricated by the quench and melt growth(QMG) technique using a vibrating sample magnetometer at 77 K. It has been found that the magnetization behavior of QMG-processed YBa2Cu3O7 can be understood in terms of Bean critical state model.
135 citations