Critical current anisotropy of GdBCO tapes grown on ISD–MgO buffered substrate

Abstract

The critical current anisotropy of a GdBa 2 Cu 3 O 7 (GdBCO) coated conductor (CC) was investigated. The MgO buffer layer was grown by the inclined substrate deposition (ISD) technique leading to a tilted c-axis growth of the GdBCO layer by 24°from the tape normal. The J c was measured in two current directions: longitudinal and transverse to the tape. The self-field J c in the 2 μm thick GdBCO layer was 1.3 MA cm −2 and 0.88 MA cm −2 at 77 K in the longitudinal and transverse directions, respectively. The 30% lower value in the transverse direction results from the current flow across the weakly superconducting layer of GdBCO. The peak in the J c -anisotropy corresponding to intrinsic pinning appears at 24°with respect to the tape surface in the longitudinal direction and the anisotropy was highly asymmetric in a wide range of fields. Due to the large crystallographic tilt of the GdBCO with respect to the tape axes, a minimum caused by vortex channeling occurred in the transverse current direction which was observed for the first time at 77 K. Another consequence of the large crystallographic tilt angle is a pronounced competing effect of the crystallographic anisotropy and Lorentz force on J c in the variable Lorentz force configuration.

Pinning Centers in ISD-MgO Coated Conductors via EB-PVD

“…716 nm in length aligned parallel to the ab-plane. Grain boundaries, marked in yellow, are visible and aligned much closer to the ab-plane than previously published for non Hf-added samples grown on ISD via EB-PVD [16].…”

“…The broad peak centered close to the tape normal (180 • -195 • ) can be attributed to pinning at grain boundaries, which are aligned, on average, in the same direction. This disappears at high fields and low temperatures [16]. Samples prepared with higher Hf content show a decrease in J c over all α compared to the undoped sample.…”

“…2(a) shows J c as a function of α for samples with a Hf content of 0 mol.%, 4.5 mol.%, 8.6 mol.% and 12.9 mol. % deposited at (660 ± 7) • C. At 77 K, 1 T, addition of 4.5 mol.% Hf shows a small increase in the minimum J c accompanied by a decrease in the peak at 61 • , which is associated with pinning at extended, correlated defects parallel to the ab-plane, such as stacking faults [16] and precipitates (see below). The broad peak centered close to the tape normal (180 • -195 • ) can be attributed to pinning at grain boundaries, which are aligned, on average, in the same direction.…”

Chemical Solution Deposition of Insulating Yttria Nanolayers as Current Flow Diverter in Superconducting GdBa2Cu3O7−δ Coated Conductors

“… 7 , 8 As a result, the distribution of the supercurrents along the length and width of the conductor becomes inhomogeneous, resulting in local variations of the critical current ( I c ) up to ±10%. 9 If the applied current is near the average I c of the conductor, zones with lower I c can locally quench. 10 The quench is characterized by a transition from the superconducting state to the resistive (normal) state.…”

“…Indeed, due to the fabrication process used to deposit and grow the REBCO film on CCs, imperfections in the microstructure, such as grain boundaries associated with misoriented grains, can affect the current percolation within the HTS layer. , As a result, the distribution of the supercurrents along the length and width of the conductor becomes inhomogeneous, resulting in local variations of the critical current ( I c ) up to ±10% . If the applied current is near the average I c of the conductor, zones with lower I c can locally quench .…”