Single crystals critical current density

Fig. 1. Cost per ampere meter for various superconducting magnet wires circles - Nb3Sn values for 106 lbs. quantity (26-27) crosses - NbTi values for present SSC spec (26) x s - 4.2 K YBaCuO value from 1.2/cm3 cost estimate and measured single crystal critical current densities at 4.2 K 81. For YBaCuO at 77 K (solid and dashed lines), a current density form J(l-H/Hc2) was used with J=105A/cm2 and Hc2 either 30 T (single crystal value for H-f-c (19)) or 6 T (H c).

Li et al. measured the critical current densities J and across the twist junction and constituent single crystals for 12 samples with different o values. They found = 1 near to Tc, as shown in... 

D. R. TURNER When the critical current density is exceeded, the film that has built up comes off almost immediately. This suggests that during the growth of the film the reaction takes place at the single crystal electrode surface, and thus the film must be very porous. 

Fig. 10.1. Critical current densities Jc for grain boundaries in YBCO films grown by epitaxy on suitably treated single crystal or bicrystal substrates, plotted against the [001] misorientation angle [10.4, 10.7, 10.51, 10.59, 10.60].

Pinning in A15 superconductors occurs at grain boundaries. This was demonstrated qualitatively by Pulver s measurements on VsSi single crystals [% where the A15 critical current densities were lower than those of polycrystalline material by a factor of 10. It is assumed that second-phase material precipitated at the grain boundaries was responsible for pinning at these sites. 

Fig. 36. Comparison of critical current densities in Y-123 thin films and single crystals, in the latter case at...

Fig. 37. Critical current density along the crystallographic c-direction H [a,b) of an Y-123 single crystal as function of fast neutron fluence. Open symbols refer to results after...

Kg. 41. Critical current densities (W c) as a liinction of field in an Y-123 single crystal irradiated with 580 MeV Sn ions to various fluences (expressed by the matching fields B ) (a) 5K, (b) 77 K. For comparison, the largest y s obtained by proton irradiation of a similar crystal are shown by the dotted lines (Civale 1997). 

Fig. 43. Effects of heavy-ion irradiation under different angles on flux pinning in Y-I23 superconductors (a) hysteresis loops at (top) 5 K and (bottom) 70 K of an Y-123 single crystal irradiated with 580 MeV Sn ions under an angle of 30° with respect to the c-axis and measured with the field at +30° or -30° from the c-axis (cf. the schematic of the field and track orientations, from Civale 1997) (b) angular dependence of the transport critical current densities in Y-123 thin films irradiated under various angles with respect to the c-axis (top parallel to the c-axis, 340 MeV Xe middle 30°, 770 MeV Pb bottom 60°, 340 MeV Xe from Kraus et al. 1994b) (c) angular dependence of the transport critical current densities in an Y-123/Pr-123 multilayer system irradiated by 770 MeV Pb ions under an angle of 30° with respect to the c-axis (Kraus et al. 1994b).

Since oxide high-temperature superconductors have a strong crystalline and electronic anisotropy, the materials must be synthesized in the form of oriented, virtually single crystal films. Furthermore, due to the extremely short coherence length of those materials, the quality of the films must be well controlled at the surface or interface as well as inside the film for device applications. The critical current density is one of the indications of the quality and the highestT obtained so far is >5 x 10 A/cm at 77K in OT. 

Fig.tt.2-32 Critical current density on dependence on the phase transformation from tetragonal to orthorhombic applied magnetic field for a single crystal film and a sintered... 

B. Roas, L. Schultz, G. Saemann-lschenko Anisotropy of the critical current density in epitaxial YBa2Cu30x films, Phys. Rev. Lett. 64, 479-482 (1990) V. Breit, P. Schweiss, R. Hauff, H. Wtihl, H. Claus, H. Rietschel, A. Erb, G. Muller-Vogt Evidence for chain superconductivity in near-stoichiometric YBa2Cu30x single crystals, Phys. Rev. B 52, R15727-R15730 (1995)... 

---