Characterization of YBCO Bulk samples by local AC-susceptometry

Melt processed HTSC bulk samples usually show a high inhomogeneity. These inhomogeneities influence application-relevant properties such as the lévitation force or the trapped field. In this contribution a technique is presented which allows investigation of these inhomogeneous properties. The measurements are performed by scanning the sample surface with a small coil system and detecting the first and third harmonic of the inductive response. The critical current density jc is calculated from the measured signal using a modified critical state model. Jcdistributions yielded by this technique are shown. © 1997 IEEE.

Development of non-weak link bulk YBCO grain boundaries for high magnetic field eegimeering applications

A non-weak link joining technique has been developed for YBCO pseudo-crystals fabricated by seeded peritectic solidification based on the formation of a liquid phase which segregates from the platelet boundaries at temperatures above = 920 °C. Electrical and magnetic measurements on these boundaries suggest that their irreversibility field can be as high as 7 T at 77 K in fully oxygenated pseudo-crystals joined along their crystallographic ab-planes which is comparable to the irreversibility behaviour of the adjacent YBCO grains. © 1999 IEEE.

The effect of dopants on the twist elastic constant and the rotational viscosity coefficient for nematics

The twist elastic constant, K2, and the rotational viscosity coefficient, γ1, are of importance when the response lime for the in-plane switching mode is studied. Since adding dopants is one technique to improve the response characteristics, the effect of dopants on these physical properties is significant. The effect on K2 and γ1 of adding alkyl(alkoxy) phenylcyclopentenones and alkyl(alkoxy) cyanobiphenyls to the base mixture ZLI-4792 together with their temperature dependence have been investigated using different temperature scales. The reduced temperature scale showed the effect of these dopants on K2 is small. On the other hand, the temperature dependence of γ1 depends on both the absolute temperature scale and the reduced temperature scale. Therefore, it is clear that the choice of temperature scale with which to compare γ1 for different systems raises fundamental questions which way not have a unique answer. 2000 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

Behavior of bulk melt-textured YBCO single domains subjected to crossed magnetic fields

We have experimentally investigated the crossed magnetic field effects on bulk melt-processed YBCO single domains. The samples were first permanently magnetized along their c-axis and then subjected to several cycles of a transverse magnetic field parallel to the ab planes. The magnetic properties along the c and ab directions were simultaneously measured using a couple of orthogonal pick-up coils as well as a Hall probe placed against the sample surface. The effects of both sweep amplitude and polarity were investigated. Field sweeps of alternate polarities are shown to affect the decay of the c-axis magnetization much more strongly than field sweeps of unique polarity do. However, the c-axis magnetization does not show any saturation even after a large number of field sweeps. Next, a micro-Hall probe scanning system was used to measure the distribution of magnetic induction over the top surface of the single domain subjected to the same combination of magnetic fields. The results are shown to be consistent with those determined with the sensing coils and bring out the role played by geometric effects.

Single domain YBCO/Ag bulk superconductors fabricated by seeded infiltration and growth

We have applied the seeded infiltration and growth (IG) technique to the processing of samples containing Ag in an attempt to fabricate Ag-doped Y-Ba-Cu-O (YBCO) bulk superconductors with enhanced mechanical properties. The IG technique has been used successfully to grow bulk Ag-doped YBCO superconductors of up to 25 mm in diameter in the form of single grains. The distribution of Ag in the parent Y-123 matrix fabricated by the IG technique is observed to be at least as uniform as that in samples grown by conventional top seeded melt growth (TSMG). Fine Y-211 particles were observed to be embedded within the Y-123 matrix for the IG processed samples, leading to a high critical current density, Jc, of over 70 kA/cm2 at 77.3 K in self-field. The distribution of Y-211 in the IG sample microstructure, however, is inhomogeneous, which leads to a variation in the spatial distribution of Jc throughout the bulk matrix. A maximum-trapped field of around 0.43 T at 1.2 mm above the sample surface (i.e. including 0.7 mm for the sensor mould thickness) is observed at liquid nitrogen temperature, despite the relatively small grain size of the sample (20 mm diameter × 7 mm thickness). © 2008 IOP Publishing Ltd.

Seeded infiltration and growth of bulk YBCO nano-composites

The seeded infiltration and growth (SIG) technique offers near-net shape processing of bulk superconductors with significant improvement in reduced Y2BaCuO5 (Y-211) inclusion size, reduced shrinkage, reduced porosity and improved current density compared to samples fabricated by top seeded melt growth (TSMG). Y2Ba4CuMOy phases where M=Nb, Mo, W, Ta, etc., have been shown to form nano-scale inclusions in the YBa2Cu3Oy (Y-123) phase matrix and to contribute to enhanced magnetic flux pinning in these materials. In this paper, we describe the introduction of Y2Ba 4CuWOy nano-scale inclusions into bulk superconductors processed by the seeded infiltration growth process. Critical current density, Jc, in excess of 105 A/cm2 at 77 K in self-field is observed for samples containing Y2Ba 4CuWOy. © 2011 IEEE.