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Description
Oxygen overdosing may be a way to further increase the critical current density of coated conductors. It has recently been shown that overdosing of of YBCO thin film coated with an Ag layer was achieved by processing at low temperature and 1 bar oxygen pressure, which allowed increasing the charge carrier density and achieving whatever high critical current 90 MA•cm−2 at 5 K, which corresponds to a fifth of the depairing current. We used commercial GdBCO and EuBCO with BHO nanorods coated conductors (CC) from Fuijkura Ltd with model numbers FYSC-S12 and FESC-SCH12 to study the effect of subsequent high pressure oxygenation (in the pressure range 1-160 bar) at temperatures 250-800 oC on charge carrier density, lattice parameters of superconducting phase and critical current density variations. Before the treatment GdBCO and EuBCO CC were all chemically treated for removing the protective Cu or Cu and Ag layers.
The evidences of overdoping were observed about what were witnessed an increase of nH(100 K), reduction of c-lattice parameters of RE123 (RE=Eu, Gd) of superconducting layers, behavior of normalized resistivity before superconducting transition, and Jc variation, however, the conditions to achieve optimal doping were not found yet. Treatment under 100 bar of oxygen for 3 h of GdBCO_CC (with Ag layer) at 600 °C led to an increase in Jc (77 K, 0 T) from 2.57 to 2.67 MA/cm2 , nH(100 K) increased from 6.551021 to 6.911021 cm-3, and Jc(5 K, 0 T) =28.94 MA/cm2 was observed after the treatment. The increase in Jc (77 K, 0 T) from 2.10 to 2.28 MA/cm2 for GdBCO_CC (without Ag layer) was observed after treatment at 300 °C under 100 bar of O2 for 3 h. In the both cases c-parameter of Gd123 decreased from 1.1735(1) to 1.1731(0) nm. For EuBCO_СС after treatment a decrease in c-parameters of Eu123 was observed: from 1.1738(8) to 1.1734(5) nm (for the Ag-coated sample under 100 bar O2 at 300 °C) and from 1.1740(2) to 1.1736(3) nm (for the sample without Ag under 160 bar O2 at 800 oC). The studies are still ongoing.
This work was supported in part by the funds from MICIU/AEI/FEDER for SUPERENERTECH (PID2021–127297OB-C21), FUNFUTURE “Severo Ochoa” (CEX2019–000917-S); MUGSUP (UCRAN20088) project from CSIC scientific cooperation with Ukraine; Catalan Government 2021 SGR 00440; and NAS of Ukraine Project III-7-24 (0788).
