Critical Current Density of YBa{2}Cu{3}O{7-d} Low-Angle Grain Boundaries in Self-Field

A large decrease is observed in the critical current density of YBCO coated conductors (CC) and related compounds when a strong perpendicular magnetic field is applied. While measurements are generally carried out at 77K only, here we present a magnetic technique permitting to determine the critical current per unit width of conductor (Icr/w) in a large temperature range. We report measurements carried out on various CCs that show that, in addition to the reduction in the cri...

Much smoother surfaces and significantly improved superconducting properties of relatively thick YBa2Cu3O7 (YBCO) films have been achieved by introducing a multilayered structure with alternating main YBCO and additional NdBCO layers. The surface of thick (1 microm) multilayers has almost no holes compared to YBCO films. Critical current density (Jc) have been drastically increased up to a factor > 3 in 1 microm multilayered structures compared to YBCO films over entire tempe...

The effects of hole content (p) and oxygen deficiency (delta) on the zero-field critical current density, Jc0, were investigated for high-quality c-axis oriented Y1-xCaxBa2Cu3O7-delta (x = 0, 0.05, 0.10, and 0.20) thin films. Low temperature critical current density of these films above the optimum doping were found to be high and were primarily determined by the hole concentration, reaching a maximum at p ~ 0.185 +/- 0.005, irrespective of the level of oxygen deficiency. Thi...

Critical current measurements were made on thin films of YBa2Cu3O7-delta and Y0.8Ca0.2Ba2Cu3O7-delta produced by sol-gel and pulsed laser deposition, respectively. Both samples have high critical currents at low temperatures and the critical current, Jc, is largest in the overdoped Y0.8Ca0.2Ba2Cu3O7-delta thin film. Annealing studies show a large increase in Jc with increasing hole concentration and suggests that the maximum Jc should occur for overdoped samples. The very ove...

The residual low angle grain boundary (GB) network is still the most important current-limiting mechanism operating in bi-axially textured rare earth barium copper oxide (REBCO) coated conductors. While Ca-doping is well established to improve super-current flow across low angle GBs in weak fields at high temperatures, Ca-doping also depresses Tc, making it so far impractical for high temperature applications of REBCO coated conductors. On the other hand, high field magnet ap...

Mechanisms of vortex dynamics and pinning and self-field effects which could account for the thickness dependence of the critical current density J_c of superconducting films are addressed. It is shown that at low magnetic fields B, the 2D single-vortex pinning and thermal fluctuations yield J_c proportional to (1/sqrt{d})exp[-(d_m/d)^{1/2}], if the film thickness d is smaller than the pinning correlation length along B. The model describes the dependence of J_c on d observed...

Temperature dependence of the zero-field critical current density, Jc0(T), in the CuO2 planes has been investigated for c-axis oriented YBa2Cu3O7-d (Y123) thin films with different hole content, p. p-values were varied by changing the oxygen deficiency, d. Jc0(T) were calculated from the magnetic hysteresis (M-H) loops obtained at different temperatures. From the analysis of the Jc0(T) data for different sample compositions, we have extracted valuable information regarding th...

For any practical superconductor the magnitude of the critical current density, $J_\textrm{c}$, is crucially important. It sets the upper limit for current in the conductor. Usually $J_\textrm{c}$ falls rapidly with increasing external magnetic field but even in zero external field the current flowing in the conductor generates a self-field which limits $J_\textrm{c}$. Here we show for thin films of thickness less than the London penetration depth, $\lambda$, this limiting $J...

For many applications of polycrystalline high-Tc superconductors the small critical currents of the grain boundaries pose a severe problem. To solve this problem we derive novel designs for the microstructure of coated conductors.

In type-II superconductors, in the regime of very high applied current density, an abrupt transition is experimentally observed from the mixed state to a highly dissipative regime, probably the normal state. This provokes a high voltage jump in the Current-Voltage Characteristics (CVC) of the samples, at a current density J* larger than the critical current Jc. In this work we study Y-123 (YBCO) microbridges sputtered over SrTiO3 substrates. We measure their CVCs for differen...