Interface Control in All MOD Coated Conductors: Influence on Critical Currents
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Interface Control in All MOD Coated Conductors: Influence on Critical Currents Alberto Pomar, Mariona Coll, Andrea Cavallaro, Jaume Gàzquez, Narcis Mestres, Felip Sandiumenge, Teresa Puig and Xavier Obradors Institut de Ciència de Materials de Barcelona, CSIC, Campus de la U.A.B., 08193 Bellaterra, Spain ABSTRACT In this work we will report our recent progress in the control of the interface quality between buffer layers and YBCO thin films grown by the trifluoroacetates route (TFA) and how it influences the critical current of the coated conductors. We have mainly focused on vacuum and metalorganic deposited (MOD) fluorite-like CeO2 buffer layers and on MOD perovskite SrTiO3 buffer layers. We will show that for vacuum CeO2 buffer layers, microcracks at the surface can be controlled by the means of thermal treatments. Coated conductors TFAYBCO/CeO2sputt/YSZ/CeO2/Ni with Jc(77K)~1MA/cm2 can be grown even in the presence of these microcracks. For MOD SrTiO3 we will show that growing the buffer layer at low temperature reduces surface roughness and multilayers with high critical currents can be achieved. An all-chemical coated conductor has been grown TFA-YBCO/SrTiO3MOD/BaZrO3 MOD /NiO-SOE/Ni with promising in-plane texture, ∆φYBCO=6.6º. For MOD CeO2 buffer layers, thermal annealings in oxidizing atmospheres lead to atomically flat surfaces that avoid the typical polycrystalline surfaces observed in MOD CeO2 grown in Ar/H2. High Jc multilayers can be achieved and the first all chemical coated conductor in IBAD tapes TFAYBCO/CeO2MOD/YSZIBAD/SS has been obtained with Jc(60K)=2.3MA/cm2. INTRODUCTION Ex-situ growth techniques are the subject of an intense research in order to get low-cost high-critical-current YBa2Cu3O7-δ (YBCO) coated conductors (CC).[1,2] In particular, the main goal is to obtain an all chemical CC where superconducting YBCO is grown by the so-called trifluoroacetates route (TFA) and the buffer layers are grown by metalorganic deposition (MOD).[1,2] To that end, several oxides have been successfully grown by MOD that can be potentially used as intermediate (as for example, La2Zr2O7, BaZrO3,…) or cap (CeO2, SrTiO3) buffer layers. On the other hand, progresses made on the optimization of TFA-YBCO growth have been impressive in the last years and the critical currents reported on single crystals or on vacuum buffer layers largely exceed the target value of 1 MA/cm2 at 77K in self-field.[3,4] Most of the studies have been focused on improving the in-plane texture of both the YBCO and the buffer layers. However, there is still a lack of studies on the role of the interface quality between the different MOD layers and the final superconducting properties of the CC. For example, it is known that several buffer properties can dramatically affect the critical current as for example, surface roughness or lattice matching with YBCO. These properties can be tuned by modifying the processing conditions of buffer layers but, for the optimization of their microstructure it is important to fully understand the r
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