Interface control in all metalorganic deposited coated conductors: Influence on critical currents
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Interface control in all metalorganic deposited coated conductors: Influence on critical currents Alberto Pomar,a) Mariona Coll, Andrea Cavallaro, Jaume Gàzquez, Narcis Mestres, Felip Sandiumenge, Teresa Puig, and Xavier Obradors Institut de Ciència de Materials de Barcelona—Consejo Superior de Investigaciones Cientificas (ICMAB-CSIC), Campus de la U.A.B., 08193 Bellaterra, Spain (Received 22 December 2005; accepted 3 May 2006)
In this work, we report recent progress in the control of the interface quality between buffer layers and YBa2Cu3O7 (YBCO) thin films grown by the trifluoroacetates route (TFA) and how it influences the critical current Jc of the coated conductors (CCs). We have mainly focused on the two most used cap layers, i.e., CeO2 and SrTiO3. We show that for CeO2 buffer layers, the key for high-quality YBCO epitaxy is to obtain atomically flat (001) terraced CeO2 surfaces. CC YBCOTFA/CeO2sputt/YSZ/CeO2/Ni with Jc (77 K) ∼ 1 MA/cm2 and chemical CC YBCOTFA/CeO2MOD/y-stabilized zirconia and ion beam assisted deposition (YSZIBAD)/stainless steel (SS) with Jc (60 K)⳱2.3MA/cm2 were obtained. For metalorganic deposited (MOD) SrTiO3 the main issue is to reduce the overall surface roughness that tends to increase film porosity due to an enhanced {100} YBCO nucleation. Improved roughness can be achieved by growing the buffer layers at lower temperatures. An all-chemical CC, YBCOTFA/SrTiO3MOD/BaZrO3MOD/NiO–SOE/Ni, with promising in-plane texture, ⌬YBCO ⳱ 6.6° was grown.
I. INTRODUCTION
To obtain low-cost high-critical-current YBa2Cu3O7−␦ (YBCO) coated conductors (CC), ex situ growth techniques have been intensively investigated.1,2 In particular, one of the main approaches is to obtain an allchemical CC in which superconducting YBCO is prepared by the so-called trifluoroacetates route (TFA) and the buffer layers are grown by metalorganic deposition (MOD).1,2 For that purpose, several oxides have been successfully fabricated by MOD that can be potentially used as intermediate (for example, La 2 Zr 2 O 7 , BaZrO3,…) or cap (CeO2, SrTiO3) buffer layers. On the other hand, progress made on the optimization of TFAYBCO growth has been impressive in recent years, and the critical current densities reported on single crystals or on vacuum buffer layers largely exceed the target value
a)
Address all correspondence to this author. e-mail: [email protected] This paper was selected as the Outstanding Meeting Paper for the 2005 MRS Spring Meeting Symposium C Proceedings, Vol. 868E. DOI: 10.1557/JMR.2006.0269 2176 J. Mater. Res., Vol. 21, No. 9, Sep 2006 http://journals.cambridge.org Downloaded: 07 Apr 2015
of 1 MA/cm2 at 77 K in self-field.3–5 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 research 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, for
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