2,595 research outputs found
Nano-composite single grain YBa2Cu3O 7-δ/Y2Ba4CuBiOy bulk superconductors
We have succeeded recently in synthesizing a chemically stable, inert family of materials of composition Y2Ba4CuMOy (Y-2411 where M Nb, Ta, Mo, W, Zr, Hf) within the superconducting YBa 2Cu3O7-δ (Y-123) phase matrix that forms effective flux pinning centers of nano-scale dimensions. In this paper we report the synthesis of the Y2Ba4CuBiOy phase with nano-scale dimensions that is similarly compatible with the Y-123 matrix and which does not impair the properties of the bulk superconductor. YBa 2Cu3O7-δ/Y2BaCuO5 (Y-123/Y-211) precursor powders enriched with various amounts of Bi 2O3 and Y2Ba4CuBiOy have been fabricated successfully in the form of large, single grains by the top seeded melt growth (TSMG) process. Microstructural studies of these composites reveal the presence of nanometer-sized Y2Ba4CuBiO y and much larger Y-211 phase particles (∼1 νm) embedded in the Y-123 phase matrix. The critical current density of the nano-composites is observed to increase significantly compared to undoped YBCO. © 2006 IOP Publishing Ltd
Behavior of bulk high-temperature superconductors of finite thickness subjected to crossed magnetic fields
Crossed magnetic field effects on bulk high-temperature superconductors have
been studied both experimentally and numerically. The sample geometry
investigated involves finite-size effects along both (crossed) magnetic field
directions. The experiments were carried out on bulk melt-processed Y-Ba-Cu-O
(YBCO) single domains that had been pre-magnetized with the applied field
parallel to their shortest direction (i.e. the c-axis) and then subjected to
several cycles of the application of a transverse magnetic field parallel to
the sample ab plane. The magnetic properties were measured using orthogonal
pick-up coils, a Hall probe placed against the sample surface and
Magneto-Optical Imaging (MOI). We show that all principal features of the
experimental data can be reproduced qualitatively using a two-dimensional
finite-element numerical model based on an E-J power law and in which the
current density flows perpendicularly to the plane within which the two
components of magnetic field are varied. The results of this study suggest that
the suppression of the magnetic moment under the action of a transverse field
can be predicted successfully by ignoring the existence of flux-free
configurations or flux-cutting effects. These investigations show that the
observed decay in magnetization results from the intricate modification of
current distribution within the sample cross-section. It is also shown that the
model does not predict any saturation of the magnetic induction, even after a
large number (~ 100) of transverse field cycles. These features are shown to be
consistent with the experimental data.Comment: 41 pages, 9 figures, accepted in Phys. Rev. B Changes : 8 references
added, a few precisions added, some typos correcte
Characterization of nano-composite M-2411/Y-123 thin films by electron backscatter diffraction and in-field critical current measurements
Thin films of nano-composite Y-Ba-Cu-O (YBCO) superconductors containing nano-sized, non-superconducting particles of Y2Ba 4CuMOx (M-2411 with M = Ag and Nb) have been prepared by the PLD technique. Electron backscatter diffraction (EBSD) has been used to analyze the crystallographic orientation of nano-particles embedded in the film microstructure. The superconducting YBa2Cu3O7 (Y-123) phase matrix is textured with a dominant (001) orientation for all samples, whereas the M-2411 phase exhibits a random orientation. Angular critical current measurements at various temperature (T) and applied magnetic field (B) have been performed on thin films containing different concentration of the M-2411 second phase. An increase in critical current density J c at T < 77 K and B < 6 T is observed for samples with low concentration of the second phase (2 mol % M-2411). Films containing 5 mol % Ag-2411 exhibit lower Jc than pure Y-123 thin films at all fields and temperatures. Samples with 5 mol % Nb-2411 show higher Jc(B) than phase pure Y-123 thin films for T < 77 K
Superconducting properties of Gd-Ba-Cu-O single grains processed from a new, Ba-rich precursor compound
Gd-Ba-Cu-O (GdBCO) single grains have been previously melt-processed successfully in air using a generic Mg-Nd-Ba-Cu-O (Mg-NdBCO) seed crystal. Previous research has revealed that the addition of a small amount of BaO2 to the precursor powders prior to melt processing can suppress the formation of Gd/Ba solid solution, and lead to a significant improvement in superconducting properties of the single grains. Research into the effects of a higher Ba content on single grain growth, however, has been limited by the relatively small grain size in the earlier studies. This has been addressed by developing Ba-rich precursor compounds Gd-163 and Gd-143, fabricated specifically to enable the presence of greater concentrations of Ba during the melt process. In this study, we propose a new processing route for the fabrication of high performance GdBCO single grain bulk superconductors in air by enriching the precursor powder with these new Ba rich compounds. The influence of the addition of the new compounds on the microstructures and superconducting properties of GdBCO single grains is reported
Enhanced self-field critical current density of nano-composite YBa(2)Cu(3)O(7) thin films grown by pulsed-laser deposition
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ EPLA, 2008.Enhanced self-field critical current density Jc of novel, high-temperature superconducting thin films is reported. Layers are deposited on (001) MgO substrates by laser ablation of YBa2Cu3O7−δ(Y-123) ceramics containing Y2Ba4CuMOx (M-2411, M=Ag, Nb, Ru, Zr) nano-particles. The Jc of films depends on the secondary-phase content of the ceramic targets, which was varied between 0 and 15 mol%. Composite layers (2 mol% of Ag-2411 and Nb-2411) exhibit Jc values at 77 K of up to 5.1 MA/cm2, which is 3 to 4 times higher than those observed in films deposited from phase pure Y-123 ceramics. Nb-2411 grows epitaxially in the composite layers and the estimated crystallite size is ~10 nm.The Austrian Science Fund, the Austrian Federal Ministry of Economics and Labour, the European Science Foundation and the Higher Education Commission of Pakistan
Single grain (LRE)-Ba-Cu-O superconductors fabricated by top seeded melt growth in air
We have recently reported a practical processing method for the fabrication in air of large, single grain (LRE)-Ba-Cu-O [where LRE Nd, Sm, Eu and Gd] bulk superconductors that exhibit high Tc and high Jc. The process is based initially on the development of a new type of generic seed crystal that can promote effectively the epitaxial nucleation of any (RE)-Ba-Cu-O system and, secondly, by suppressing the formation of (LRE)/Ba solid solution in a controlled manner within large LRE-Ba-Cu-O grains processed in air. In this paper we investigate the degree of homogeneity of large grain Sm-Ba-Cu-O superconductors fabricated by this novel process. The technique offers a significant degree of freedom in terms of processing parameters and reproducibility in the growth of oriented single grains in air and yields bulk samples with significantly improved superconducting and field-trapping properties compared to those processed by conventional top seeded melt growth (TSMG)
Unusual microwave response and bulk conductivity of very thin fese0.3te0.7 films as a function of temperature
Results of X-band microwave surface impedance measurements of FeSe1-xTex very
thin film are reported. The effective surface resistance shows appearance of
peak at T less and near Tc when plotted as function of temperature. The authors
suggests that the most well-reasoned explanation can be based on the idea of
the changing orientation of the microwave magnetic field at a SN phase
transition near the surface of a very thin film. The magnetic penetration depth
exhibits a power-law behavior of delta lambda proportional to T with an
exponent n = 2.4 at low temperatures, which is noticeably higher than in the
published results on FeSe1-xTexsingle crystal. However the temperature
dependence of the superfluid conductivity remains very different from the
behavior described by the BCS theory. Experimental results are fitted very well
by a two-gap model with delta1/kTc=0.43 and delta2/kTc=1.22,thus supporting
s(+-)- wave symmetry. The rapid increase of the quasiparticle scattering time
is obtained from the microwave impedance measurements.Comment: 13 pages, 13 figure
Growth rate of YBCO single grains containing Y-2411(M)
Y-Ba-Cu-O (YBCO) single grains have the potential to generate large trapped magnetic fields for a variety of engineering applications, and research on the processing and properties of this material has attracted world-wide interest. In particular, the introduction of flux pinning centres to the large grain microstructure to improve its current density, Jc, and hence trapped field, has been investigated extensively over the past decade. Y 2Ba4CuMOx [Y-2411(M)], where M = Nb, Ta, Mo, W, Ru, Zr, Bi and Ag, has been reported to form particularly effective flux pinning centres in YBCO due primarily to its ability to exist as nano-size inclusions in the superconducting phase matrix. However, the addition of the Y-2411(M) phase to the precursor composition complicates the melt-processing of single grains. We report an investigation of the growth rate of single YBCO grains containing Y-2411(Bi) phase inclusions and Y2O3. The superconducting properties of these large single grains have been measured specifically to investigate the effect of Y2O3 on broadening the growth window of these materials
Fluktuacije faze supravodljivog uređenja u osnovnom stanju kao preduvjet jakih kritičnih fluktuacija u visokotemperaturnim supravodičima
We analyse the reversible magnetisation and heat capacity of YBa2Cu3O7−δ in the “vortex liquid” state and find that both properties are reasonably well described by the 3D XY critical-fluctuation model. The free-energy density in the “vortex liquid” state has a particularly simple form over a wide range of fields (H) and temperatures (T). This leads us to a picture in which the presence of critical fluctuations in high-Tc superconductors is directly linked to the remarkably small number of overlapping Cooper pairs at T=0 and H=0 rather than low dimensionality or high temperatures.Analiziramo reverzibilnu magnetizaciju i toplinski kapacitet YBa2Cu3O7−δ u stanju “tekućine vrtloga”, i nalazimo da su oba svojstva razumno dobro opisana 3D XY modelom kritičnih fluktuacija. U velikom području polja (H) i temperatura (T), gustoća slobodne energije u stanju “tekućine vrtloga” ima osobito jednostavan oblik. To nas vodi do slike u kojoj je prisustvo kritičnih fluktuacija u visokotemperaturnim supravodičima neposredno povezano s vrlo malim brojem prekrivajućih Cooperovih parova pri T =0i H = 0, prije nego s niskom dimenzionalnošću ili visokim temperaturama
Fluktuacije faze supravodljivog uređenja u osnovnom stanju kao preduvjet jakih kritičnih fluktuacija u visokotemperaturnim supravodičima
We analyse the reversible magnetisation and heat capacity of YBa2Cu3O7−δ in the “vortex liquid” state and find that both properties are reasonably well described by the 3D XY critical-fluctuation model. The free-energy density in the “vortex liquid” state has a particularly simple form over a wide range of fields (H) and temperatures (T). This leads us to a picture in which the presence of critical fluctuations in high-Tc superconductors is directly linked to the remarkably small number of overlapping Cooper pairs at T=0 and H=0 rather than low dimensionality or high temperatures.Analiziramo reverzibilnu magnetizaciju i toplinski kapacitet YBa2Cu3O7−δ u stanju “tekućine vrtloga”, i nalazimo da su oba svojstva razumno dobro opisana 3D XY modelom kritičnih fluktuacija. U velikom području polja (H) i temperatura (T), gustoća slobodne energije u stanju “tekućine vrtloga” ima osobito jednostavan oblik. To nas vodi do slike u kojoj je prisustvo kritičnih fluktuacija u visokotemperaturnim supravodičima neposredno povezano s vrlo malim brojem prekrivajućih Cooperovih parova pri T =0i H = 0, prije nego s niskom dimenzionalnošću ili visokim temperaturama
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