HTS Samples Research Articles

One-step reaction and consolidation of Hg based high-temperature superconductors by hot isostatic pressing

A hot isostatic press (HIP) techniques has been used successfully to react and consolidate in one step the Hg based high-temperature superconductors (HTS's). Hot isostatic pressing (HIPping) overcomes some of the problems encountered in the quartz encapsulation technique typically used to make Hg based HTS samples, such as containing the high vapor pressures of Hg and avoiding explosions. The HIPping conditions for processing (i.e., range of temperature and pressure) are significantly different from those used in the quartz-encapsulation method. These differences seem to relax the stringent conditions on precursor processing required in other processing methods. Hg based HTS samples were successfully made from both nitrate and carbonate precursors, as well as from commercially available precursors. X-ray diffraction experiments indicated that the best materials were made with nitrate precursors and were composed of 1223 phase (66%), 1212 phase (33%) and a small amount of BaCuO 2 (1%). We have HIPped powders and contained them in selected high-purity metal foils. We find that Au is a good containment material for processing as it reacts very little with the Hg compounds being formed. Ag, on the other hand, reacts extensively. Samples with densities as high as 97% of theoretical density were formed. This technique has been used to successfully fabricate component that may lead directly to devices.

The effect of hot isostatic pressing on the microstructure and critical current density of directional solidified YBa2Cu3Ox superconductors

YBa2Cu3Ox (123) high-temperature superconductors (HTSS) obtained by conventional directional solidification have been shown to be capable of carrying substantial critical currents (lc), and can be used in practical applications such as current leads. When these multidomained HTSS are subjected to thermal shock, however, the lc is found to be degraded. In order to ascertain the cause of this decrease, microscopic studies have been performed. The results indicate that the decrease in lc can be linked to the generation and propagation of microcracks between the a-b plane grain boundaries. Hot isostatic pressing (HIPing) has been found to be effective in eliminating this degradation, and the lc of HIPed HTS samples is no longer sensitive to thermal cycling. Microstructural observations revealed that HIPing resulted in a reduction in the amount and the size of microcracks as compared with thermally cycled HTSS. Moreover, large macrocracks are found to be bridged by reaction products. The healing of microcracks and the strengthening of a-b plane grain boundaries as well as the transformation of macrocracks are believed to be responsible for the improved superconducting and mechanical stability of the HIPed HTSS.

Characterizing the S/N transition of VAMAS HTS samples

As a part of a VAMAS program, the S/N transition of short sample HTS conductors were studied for a range of fields and temperatures. This paper discusses the characterization of typical and damaged samples at 4.2 K and 0 T. Attention is given to the calculation of n-values and the first derivative of the V-I curves. Also, the measurement setup is explained in some detail. >

Some features of magnetic and superconducting properties of 1-2-3 ceramic in low frequency electromagnetic field

It is found that the frequency dependence R(f) of the resistance of HTS samples at T< T c is nonmonotomic in the range 0 – 10 8 Hz. It is also found that the dc magnetic field produces different influence on different parts of the R(f) dependence.

Critical processing parameters for bulk and wire high temperature superconductors for applications (invited) (abstract)

To make true large applications of high temperature superconductors (HTS’s), one requires not just a large critical current density (Jc) and high transition temperature (Tc), but also large total current (Ic is the JcA, where A is the cross sectional area) and large total current length (Icl where l is the length) of an HTS which can be further shaped into a usable form, e.g., disk, bar, cylinder, or wire. The large anisotropy, short coherence length, and large penetration depth of HTS’s pose serious challenges to efforts to enhance the Jc, Ic, or Icl of HTS’s. Melt-texturing technique by slow cooling through the peritectic temperature has proven to be effective in removing large-angle grain boundaries detrimental to Jc in HTS samples of small size; but many problems remain. The short coherence length reduces the pinning potential for magnetic fluxoids and also renders ineffective the nonsuperconducting dispersion in the HTS matrix to enhance pinning through the conventional metallurgical method. Defects of atomic scale acting as pinning centers to raise Jc have been obtained through irradiation by high energy particles and in situ chemical decomposition. However, in most of these studies Jc was determined only by magnetic measurements, not by transport techniques. We have therefore carried out a systematic study on the melt-texturing of HTS’s in both bulk and wire forms. We have identified major processing parameters in reducing the microcracks, increasing the dimensions of the bulk HTS, controlling the grain alignment, improving the chemical homogeneity, enhancing the processing rate, and controlling the epitaxial growth of HTS’s in an Ag sheath. Effects of irradiation by various types of particles of different energies on Jc determined both by magnetic and transport techniques have also been examined. These results will be presented and discussed, following a brief review on the current status of bulk and wire processing of HTS’s.

Electrical Resistivity and XRD Measurements on YBCO–PbS HTS System

Electrical resistivity and XRD measurements are reported for HTS samples with starting composition Y1Ba2(Cu1−xPbx)3S3xOy(0 ≦ x ≦ 0.20). It is elucidated that the substituted compounds (0 0.05 samples, however, the evolution of impurity phases like Y2Ba1Cu1O5 and BaPbO3 suppresses the supercbnducting properties. The probable explanation of these results is also discussed. It is found that perhaps the sulphur of PbS substitutes for oxygen in the YBCO-lattice, however, Pb does not, it mainly forms the impurity phase BaPbO3.

Trapped magnetic field and critical current density in melt-textured Y-Ba-Cu-O superconductors

Abstract The spatial distribution of the trapped magnetic field in melt-textured Y-Ba-Cu-O (MT-Y123) materials has been studied. Granular structures in MT-Y123 samples can be observed directly by a field mapping method. A phenomenological current model has been developed to account for the trapped field intensity and profile in HTS samples. Measurements of magnetic moments by VSM, and by trapped field profiles in MT-Y123 samples are discussed.