Y.F. Zhang

Flux pinning properties in a GdBa2Cu3O7−δ bulk superconductor with the addition of magnetic alloy particles

Pinning stability and the introduction of pinning centers are essential problems in the application of high temperature superconductors. A study of the role of the addition of a variety of oxides into Gd-123 bulk superconductors was pursued with respect to the effect of magnetic pinning centers on enhancement of critical current density. We have found the addition of magnetic alloy particles into Gd-123 bulk contributes to the enhancement of the critical current density under a magnetic field. The magnetic particles of Fe–B alloy with small amounts of Cu–Nb–Si–Cr were added into the Gd123 matrix and grown into single-domain bulk in air. The effects of Fe–B alloy magnetic particles on the superconducting pinning properties of Gd123 bulk are reported. The experimental results showed that the Tc of the bulk was suppressed significantly and the transition width became larger with an increase in the doping content of the magnetic particles. This was consistent with magnetic impurities suppressing superconductivity. The critical current density deduced from the magnetization as a function of applied external magnetic field was enhanced under low magnetic field and high magnetic field, which is different from the bulk doped with paramagnetic particles. Possible mechanisms and the role of magnetic materials from the viewpoint of increased flux pinning inside the bulk are discussed.

Melt-growth bulk superconductors and application to an axial-gap-type rotating machine

The present manuscript addresses key issues in the course of our study of materials processing of bulk high-temperature superconductors, trapped flux and its application to a prototype axial-gap-type rotating machine. The TUMSAT group has conducted a series of studies since 2003 on the growth of GdBa2Cu3O7−δ bulk material and its application in a compact low-speed high-torque rotating machine. In the stage of material growth, gaining the advantage of a large motive torque density requires large integrated flux in the motor/generators. A large grain surface might be required with sophisticated techniques for the melt-growth texture in the bulk with optimal flux pinning. In the second stage, the in situ magnetization procedure for bulk superconductors in the applied machine is a crucial part of the technology. Pulsed current excitation by using an armature copper winding has magnetized field pole bulks on the rotor. The axial-gap flux synchronous machine studied in the past decade is a condensed technology and indicates that further scientific development is required for a future compact machine to be superior to conventional ones in accordance with the cryogenic periphery and flux stabilization.

Effect of addition of soft magnetic alloy particles on the flux trapping in Gd123 bulk superconductors

Pinning stability and the introduction of magnetic flux pinning is an essential problem in applications of high-Tc superconductors. Study on the role of addition of a variety of metal oxides into GdBa2Cu3O7−δ (Gd123) bulk superconductors was carried out. We found that the addition of 0.05 wt. % of soft magnetic alloy particles Fe-Cu-Nb-Si-Cr-B (Fe-B) into the Gd123 contributes to the enhancement of the critical current density (Jc) under a wide range of applied magnetic fields up to 3 T. The Fe-B particles refined less than 10 μm by ball milling indicate no remarkable contribution on the Jc under the magnetic field. The reduction of the Ba content resulted in the appearance of a peak of Jc which has been observed in the Gd/Ba solid solution with rich Ba content. These results let us discriminate the effect of the magnetic particles from other conventional flux pinning mechanism. The peak of Jc under magnetic field was not only observed in the part along the c-axis under the seed of the sample but also in the growth sector around the periphery of the Gd123 bulk with Fe-B addition. It indicates that the magnetic particles inclusions play an important role on the homogeneous enhancement of Jc and the high flux pinning performance.

Enhanced performance in bulk superconductor GdBa2Cu3O7- with additions of -Fe2O3 particles

By using a top seeding melt-textured growth process, single domain GdBa2Cu3O7−δ superconductor bulks with variable additions of oxide particles α-Fe2O3 were prepared in air. The effect of the α-Fe2O3 additions on the superconductivity properties was investigated. An increase of the critical current JC in low and moderate fields at 77 K was observed by adding tiny amounts of the α-Fe2O3 particles. The superconductor properties were not suppressed after the addition of the particles, with the superconducting transition temperature around 93.5 K. The present report showed that the α-Fe2O3 oxide particles may be embedded in the GdBa2Cu3O7−δ matrix to form the pinning center to enhance the critical current and the trapping field. With increasing α-Fe2O3 particles, however, the superconductor transition temperature shifts to 93 K and the critical current decreases.

Microstructure and superconducting properties in air-properties GdBa2Cu3O7-δ superconductor with the additives of nano particles

It is regarded as an effective method to improve the flux pinning performance by the additives of the secondary phase inclusions in nano sizes into high temperature superconductor bulks. We prepared the single domain superconductor GdBa2Gi3O7-δ bulks with variable additions of (ZrO2+SnO2+ZnO) nano-particles in air by using top seed melt-textured growth process. The effect of nano-particle additions on superconductivity properties has been investigated. An enhancement of the critical current JC in low and intermediate field at 77K and trapped field was discovered by the additions of the nano-particles. At the same time, the superconductor transition temperature, TC, slightly decreases from 93.5K to 91.5K The microstructure measurements show that the nano-particle inclusions enhance with the increase of the content of nano-particles, which may illuminate the JC enhancement of the specimens.