Search

The primary prerequisite for successful single grain growth of a REBa2Cu3Oy bulk superconductor is the determination of an optimized growth temperature window of the given system. In our recent work, addition of 20 wt. % of Dy2BaCuO5 (Dy-211) to the GdBa2Cu3O7-δ bulk sample [(Gd,Dy)BCO] enhanced superconducting properties. Then, different isothermal dwell times were tested at various undercooling temperatures to find the temperature window appropriate for the single grain growth by a top-seeded infiltration growth process performed in air. Nearly perfect single-grain (Gd,Dy)BCO crystals were grown. A systematic and detailed investigation of the microstructure, composition, and physical properties of the single-grain (Gd,Dy)BCO superconductors was carried out. The superconducting transition was sharp with the onset at 92.9 K. The field dependence of the critical current density (Jc) was determined at several temperatures. At 77 K, a self-field Jc of 55 kA/cm² and a trapped field of 0.19 T were achieved. The possibilities for further improvement of the microstructure and superconducting performance are discussed. [ABSTRACT FROM AUTHOR]

The effects of adding low-melting point metals (Pb, Sn, In and Ge) to polycrystalline CaKFe4As4 (CaK1144) superconductors were investigated. We found that Sn is the most stable with CaK1144 among these low-melting point metals. Synthesis conditions as well as the doping quantity of Sn were optimized, and phase stability, microstructures and superconducting properties were investigated. At the optimized sintering temperature of 700 °C, Sn was effectively solidified in grain boundaries (GBs) of the CaK1144 bulk samples and secondary phase formations were not serious in optimized samples. As the Sn amount increased, filling of Sn in the GBs increased up to 30 wt% with homogeneous dispersion. The magnetic field dependence of critical-current density (Jc) was significantly enhanced by 30 wt% Sn addition and decreased with further increase of Sn addition. The filling up of 1144 grain boundaries by the optimal amount of Sn enhanced the Jc from 11.7 kA cm−2 to 21.7 kA cm−2 in a self-field and at 4.2 K. Sn addition was effective both to suppress the impurity phases as well as increase Jc of CaK1144. [ABSTRACT FROM AUTHOR]

A high density CaKFe4As4 bulk sample was successfully synthesized using a spark plasma sintering (SPS) technique. The density of the synthesized sample was 5.02 g cm−3, corresponding to 96.2% of the theoretical density of CaKFe4As4. Moreover, a reasonably high Vickers hardness of 1 GPa was measured. The electrical resistivity of the SPS bulk sample was as low as approximately 600 μΩ cm at 300 K, which is smaller than that of the ordinary sintered polycrystalline sample by nearly one order of magnitude, and exhibited a sharp superconducting transition with the transition width (ΔTc) less than 2 K, indicating an improved grain connectivity. The critical current density of the SPS bulk sample calculated from the magnetization hysteresis loops (magnetic Jc) reached 18 kA cm−2 at 4.2 K under 5 T, which is the highest among the iron-based superconductor polycrystalline samples reported thus far. [ABSTRACT FROM AUTHOR]

The sintering temperature for the production of Y3Ba5Cu8O18 (Y-358) preform powders synthesized in sol-gel spontaneous combustion technique was optimized. A large single-grain bulk Y-358 crystal was fabricated employing a top-seeded melt-growth technique utilizing the optimally sintered preform powders (i.e., at 900 ∘C for 12 h). Structural, microstructural, elemental, and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscopy, and SQUID, respectively. The structural characterization indicated that the sample is highly textured in (00l) direction. The Y-358 phase fractions were estimated in both preform powders and bulk sample using Rietveld refinement. The onset of superconducting transition is observed at 92.5 K, and the curve is very sharp indicative of the high quality of the produced bulk sample. The field dependence of critical current density (Jc) was determined at 77 K, and the self-field Jc was found to be ∼26 kA/cm2. A magnetic field of 0.27 T was trapped by the sample at 77 K. [ABSTRACT FROM AUTHOR]

The sintering temperature for the production of Y3Ba5Cu8O18 (Y-358) preform powders synthesized in sol-gel spontaneous combustion technique was optimized. A large single-grain bulk Y-358 crystal was fabricated employing a top-seeded melt-growth technique utilizing the optimally sintered preform powders (i.e., at 900 ∘C for 12 h). Structural, microstructural, elemental, and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscopy, and SQUID, respectively. The structural characterization indicated that the sample is highly textured in (00l) direction. The Y-358 phase fractions were estimated in both preform powders and bulk sample using Rietveld refinement. The onset of superconducting transition is observed at 92.5 K, and the curve is very sharp indicative of the high quality of the produced bulk sample. The field dependence of critical current density (Jc) was determined at 77 K, and the self-field Jc was found to be ∼26 kA/cm2. A magnetic field of 0.27 T was trapped by the sample at 77 K. [ABSTRACT FROM AUTHOR]

Superconductivity in a low dimensional structure is an interesting phenomenon both from fundamental and application point of view. The present study proposes a novel method of fabricating single crystalline YBa2Cu3O7-δ (YBCO/Y123) nanorods from the nitrate solution containing Yttrium (Y), Barium (Ba) and copper (Cu) ions in stoicheometric proportion to that of Y123. The nitrate solution was soaked into cellulose and then was heated to a phase formation temperature of 880 °C with a dwell of 6 and 24 hours followed by oxygenation for 100 hours at 460 °C. Fine particles of YBCO, sintered together to form long (>100 μm) thread like structure with a diameter of ~2 μm were observed. At higher magnification nano-rods with ~ 50-100 nm diameters and length of ~500 nm were observed for 24 hours heat treated sample. Selective area electron diffraction was done on these nanorods and was compared with the simulated pattern of YBCO. A broad diamagnetic, transition in magnetic susceptibility below 90 K indicates the presence of superconductivity. M-H loops recorded at 77 K on these samples indicate superconducting behavior at low fields and paramagnetic behavior at high fields. M-H loops above superconducting transition (90 K-300 K) unveil the ferromagnetism in these samples. [ABSTRACT FROM AUTHOR]