A La2−xGdxZr2O7 layer deposited by chemical solution: a promising seed layer for the fabrication of high Jc and low cost coated conductors

We deposited La2−xGdxZr2O7 seed layers by a chemical solution method on a Ni–5%W substrate to study the influence of these layers on the growth process of a 60 nm-thick La2Zr2O7 layer. We measured the performances of these new buffer layers integrated in a coated conductor with a 300 nm-thick Y0.5Gd0.5Ba2Cu3O7−x layer. For the seed layers, we considered two different gadolinium contents (x = 0.2 and x = 0.8) and three different thicknesses for these compositions (20 nm, 40 nm, and 60 nm). The most promising buffer layer stacks are those with 20 nm of the La1.8Gd0.2Zr2O7 layer or La1.2Gd0.8Zr2O7. Indeed the La2−xGdxZr2O7/La2Zr2O7 films are highly textured, similar to a 100 nm-thick La2Zr2O7 layer, but their roughness is four times lower. Moreover they contain less and smaller pores in the seed layer than a pure La2Zr2O7 layer. The surface of La2Zr2O7 is also homogenous and crystalline with an orientation deviation from the ideal 〈011〉 (100) direction below 10°. With the 20 nm La2−xGdxZr2O7 seed layers we obtain in the coated conductors an efficiently textured transfer with no gradual degradation from the substrate throughout the superconducting layer. The highest Tc and Jc values are achieved with the La1.8Gd0.2Zr2O7 layer and are, respectively, 91 K and 1.4 MA cm−2. This trend seems to be due to an improvement of the surface quality of the Ni5%W substrate by the addition of a thin seed layer. Our results offer the potential of the La2−xGdxZr2O7 seed layers as promising alternatives for the classic Ni–5%W/LZO/CeO2/YBCO architectures.