N. Zhu

microstructure and critical current density of zone melt textured YBa2Cu3O6+x

Zone melting has been used to produce texture in extruded YBa2Cu3O6+x wires. Highly aligned microstructures are produced with a‐b planes oriented along the axis of the wires. Microstructural observations show that changes in alignment orientation can occur, and can result in the inability to carry a transport current. Pulsed transport Jc measurements on oriented samples indicate a zero field critical current density greater than 4×104 A/cm2.

Texture processing of extruded YBa2Cu3O6+x wires by zone melting

Abstract Zone melting has been used to produce texture in extruded YBa 2 Cu 3 O 6+ x wires. By controlling the directional solidification of the molten zone, oriented structures are produced that show a large magnetic hysteresis at 77 K compared to unaligned extruded YBa 2 Cu 3 O 6+ x wires. A magnetization critical current density of 1.8 × 10 4 A/cm 2 in an applied field of 20 kOe has been achieved.

Microstructure and critical current density of zone melt textured YBa2Cu3O6 + x with Y2BaCuO5 additions

Abstract Extruded wires of YBa 2 Cu 3 O 6 + x With Y 2 BaCuO 5 (211) additions were zone melted to produce textured microstructures. Excess 211 was introduced in order to observe its effect on the transport properties and the microstructure. Highly aligned microstructures can be produced with a−b planes oriented along the axis of the wires. 211 additions appear to modify the microstructure, with YBCO platelet thickness decreasing with increasing 211 additions. Magnetization and transport measurements show a decrease in J c with increasing 211 additions.

Microstructure and critical current density of zone melt textured YBa2Cu3O6+x/Y2BaCuO5 with BaSnO3 additions

Additions of BaSnO3 have been made to YBa2Cu3O6+x/Y2BaCuO5 composite wires to examine its potential for improving solidification processing and enhancing pinning. Zone melting has been used to produce texture in extruded YBa2Cu3O6+x (Y‐123) wires with Y2BaCuO5(211) and BaSnO3 additions. BaSnO3 additions markedly improve the magnetization properties over similarly textured Y‐123 or Y‐123+211 wires in low fields, but do not show a noticeable improvement at higher fields (≳2 T). Microstructural effects of BaSnO3 include the growth of much larger Y‐123 grains, and a substantial reduction in size of 211 precipitates. Magnetic critical current densities (Jc) in excess of 1.2×105 A/cm2 in zero field, and 3.0×104 A/cm2 at 1 T are observed.

Zone melt texturing of YBa2Cu3O6+x with silver additions

Abstract Extruded YBa 2 Cu 3 O 6+ x wires containing 0 to 15 vol% silver have been textured by a zone melting process. It is observed that the magnetization critical current density in textured samples decreases with silver additions, unlike what is usually observed in sintered samples. In transport measurements, a J c of 5500 A/cm 2 in an applied field of 8000 Oe was observed in a sample containing 15 vol% silver.

Microstructure and magnetic properties of zone melt textured YBa2Cu3O6+x with BaSnO3 additions

Abstract The effect of BaSnO 3 additions on the microstructure and magnetic properties of zone melt textured YBa 2 Cu 3 O 6+ x (YBCO) wires has been investigated. BaSnO 3 additions improve the magnetization properties over similarly textured YBCO wires in low fields, but do not show a noticeable improvement at higher fields (> 2 T). Microstructural effects of BaSnO 3 include a reduction in size of 211 precipitates and a decrease in the YBCO platelet width. Magnetic critical current densities ( J c ) in excess of 8 × 10 4 A/cm 2 in zero field, and 2.0 × 10 4 A/cm 2 at 1 T are observed. The improvement in low field properties are observed to peak at a YBCO:BaSnO 3 molar ratio of 3:1, and then degrade with additional BaSnO 3 additions.

Flux creep and pinning potential distribution in zone‐melted YBa2Cu3Ox

Magnetic relaxation data have been taken on zone‐melted and sintered YBa2Cu3Ox samples over wide temperature and magnetic field ranges. We have found that magnetic relaxation varies greatly in the samples with different microstructures and crystallographic orientations. Flux‐creep rates have been found to be reduced in the zone‐melted samples owing to large amounts of intragranular crystal defects such as edge dislocations and stacking faults. An important flux‐pinning behavior related to the pinning potential distributions has been observed in the samples. The relationship between microstructural orientation and pinning potential distributions in YBa2Cu3Ox is discussed.

Magnetic relaxation and flux pinning in zone melt textured YBa2Cu3O6+x

Abstract The zero field cooled magnetic relaxation and the remnant magnetization as a function of applied magnetic field were studied for zero melt textured YBa 2 Cu 3 O 6+ x . The pinning potential was calculated from the flux creep rate of the zero field cooled magnetization. It was found that there is a strong correlation between the field dependency of the pinning potential and the critical current which essentially supports the line pinning model of Smith et al. [1].

Texturing of YBa2Cu3O6+x by melt processing

Solidification from the melt is an effective method for producing high-critical-temperature superconductors that are highly textured and have relatively high critical current densities. There are various means to generate a textured microstructure, but in all techniques the proper control of solidification parameters is paramount.

Observation of attractive forces in zone-melted YBa2Cu3O7−x

Abstract Attractive forces between zone-melted YBa 2 Cu 3 O 7− x (YBCO) samples and a magnet beneath the samples were observed. Attractive forces were observed only among the samples with large magnetic hysteresis loops. The magnitude of the observed attractive forces is related to the samples critical current density, J c , and the magnetic flux gradient the sample experiences.