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

Abstract

We deposited La_2−xGd_xZr₂O₇ 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 Y_0.5Gd_0.5Ba₂Cu₃O_7−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 La_1.8Gd_0.2Zr₂O₇ layer or La_1.2Gd_0.8Zr₂O₇. Indeed the La_2−xGd_xZr₂O₇/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 La_2−xGd_xZr₂O₇ 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 T_c and J_c values are achieved with the La_1.8Gd_0.2Zr₂O₇ 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 La_2−xGd_xZr₂O₇ seed layers as promising alternatives for the classic Ni–5%W/LZO/CeO₂/YBCO architectures.