La1− x Mn1− y O3± δ buffer layers on inclined substrate deposited MgO templates for coated conductors

Abstract

Most commercial high-temperature superconducting coated conductors based on ion beam assisted MgO deposited templates use LaMnO₃ (LMO) films as the terminating buffer layer. In contrast, coated conductors based on inclined substrate deposition (ISD)-MgO technology are still produced with homoepitaxial (homoepi)-MgO as the cap layer. In this work we report on the deposition of LMO buffer layers on ISD-MgO/homoepi-MgO by electron beam physical vapor deposition. The growth parameters of textured LMO films were studied systematically and their properties were optimized regarding the critical current densitiy (J_c) of the subsequently deposited DyBa₂Cu₃O_7-δ (DyBCO) superconducting films. LMO films without outgrowths at the surface were obtained at growth rates of up to 4 Å/s. Despite the formation of non-stoichiometric LMO films containing 59 % La, single-phase films were obtained at substrate temperatures below 775 C and at oxygen partial pressures of up to 4×10^-4 mbar due to a large homogeneity region towards La. The J_c values of DyBCO films deposited on LMO were found to be independent of the LMO thickness in a range from 50 nm to 450 nm. DyBCO films on LMO reach J_c = 0.83 MA/cm² at 77 K in zero applied field. This value is up to 30 % higher than those of DyBCO films grown directly on homoepi-MgO. The wide range of LMO growth parameters and higher J_c values of DyBCO on LMO compared to DyBCO on homoepi-MgO make this material attractive for its use in manufacturing coated conductors based on ISD-MgO technology.