High critical current density in YBCO coated conductors prepared by thermalco-evaporation

Abstract

We report on the in situ preparation ofY Ba2Cu3O7−δ films uniformly depositedover large areas,>20 × 20 cm2, at 690 °C by thermal co-evaporation onto Ni–5 at.% W biaxially textured tapes buffered with e-beam evaporatedCeO2. Typically, the thickness of the YBCO andCeO2 layerswas 0.9 and 0.1 µm, respectively. Deposition rates were 0.2 and2.5 nm s−1, respectively.X-ray diffraction θ–2θ Bragg–Brentano and pole figure measurements, and Nomarsky opticaland SEM microscopy analysis show good biaxial texture of both layers,sharp interfaces and the absence of cracks. Midpoint critical temperatures,Tc, fall reproducibly in the 87–88 K range with transition widthsΔTc = 1 K. Remarkably high transport critical current densities,Jc, in the2.0–2.5 MA cm−2 range are achieved at 77 K in 1 cm long samples. The above deposition route appears to bepromising for the development of long-length YBCO coated conductors thanks to therelatively low deposition temperature, the high degree of uniformity over large areas andthe simple single buffer layer architecture.