Epitaxial NiO buffer layer by chemical enhanced surface oxidation epitaxy on Ni–5%W RABiTS for YBCO coated conductors

Abstract

For the deposition of YBa 2Cu 3O 7− δ (YBCO) on metallic substrates like Ni-based rolling assisted biaxially textured substrates (RABiTS), buffer layers (e.g. NiO, CeO 2, Y-stab. ZrO 2) are necessary. In the beginning of the deposition process of oxide layers, often the formation of misoriented NiO (especially NiO(1 1 1)) is observed. It has been shown that a biaxially textured (0 0 1)-oriented NiO buffer layer can be grown by Surface Oxidation Epitaxy (SOE) at high temperatures (⩾1000 °C) on many Ni-based RABiTS including micro-alloyed Ni, NiCr or NiV. RABiTS with high W content show very good mechanical properties but reveal some problems using the SOE method for producing a NiO buffer layer suitable for YBCO coated superconducting tapes. We found a chemical pretreatment which makes it possible to grow (0 0 1)-oriented, biaxially textured NiO buffer layers on Ni with high (5%) W content at temperatures ranging from 320 °C to 1300 °C and at ambient air. In this paper we report the influence of the chemical pretreatment, the oxidation time and the oxidation temperature on the properties of self oxidized NiO layers as well as the influence of the oxidation process on the substrate properties. By the deposition of a subsequent La 0.7Ca 0.3MnO 3 (LCMO) buffer layer, YBCO was grown epitaxially on Ni–5%W-RABiTS with first results showing a critical current density J c of 1 × 10 5 A/cm 2 and a critical temperature T c of 89 K.