Deposition of rare earth tantalate buffers on textured Ni-W substrates for YBCO coated conductor using chemical solution
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A. Goyalb) and L. Heatherly, Metals and Ceramics Divison, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
D.B. Beach Chemical Sciences Divison, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6100
Epitaxial films of rare-earth (RE ⳱ La, Ce, Eu, and Gd) tantalates, RE3TaO7 with pyrochlore structures were grown on biaxially textured nickel-3 at.% tungsten (Ni-W) substrates using chemical solution deposition (CSD) process. Precursor solution of 0.3∼0.4 M concentration of total cations were spin coated on to short samples of Ni-W substrates and the films were crystallized at 1050∼1100 °C in a gas mixture of Ar- 4% H2 for 15 to 60 min. X-ray studies show that the films of pyrochlore RE tantalate films are highly textured with cube-on-cube epitaxy. Improved texture was observed in case of lanthanum tantalate (La3TaO7) film grown on Ni-W substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigations of RE3TaO7 films reveal a fairly dense and smooth microstructure without cracks and porosity. The rare-earth tantalate layers may be potentially used as buffer layers for YBa2Cu3O7-␦ (YBCO) coated conductors.
I. INTRODUCTION
Thin films with pyrochlore structures have been used as potential buffer layers for YBa2Cu3O7-␦ (YBCO) coated conductors, due to their thermal stability and their chemical and structural compatibility with the substrates and superconducting layers.1 Due to the extensive compositional range of the compounds which exhibit the pyrochlore structure with an A2B2O7 stoichiometry,2 there are a variety of actual and potential applications for these materials. Examples include: dielectric materials,3,4 catalysts, 5,6 solid electrolytes, 7–9 thermal-barrier coatings10,11 as well as actinide host phases for nuclear waste encapsulation.12–15 The pyrochlore structure under study has the chemical formula A3BO7, where A (Lu to La) is a larger trivalent and B (Ta) is a pentavalent cation. During the last two decades, lot of effort has been made to prepare superconducting YBCO-coated conductors using different physical and chemical deposition methods. Such conductors generally consist of a YBCO
a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/publications/jmr/policy.html. DOI: 10.1557/JMR.2006.0099
film grown on a metallic substrate with intermediate buffer layers. Buffer layers act as chemical barriers between the YBCO layer and the substrate to prevent the metal diffusion into YBCO as well as the oxidation of the metallic surface during YBCO film deposition. Highly textured YBCO films are essential to obtain high critical currents. In the Rolling-assisted bi-axially textured substrates (RABiTS) approach, starting from a perfect textured metallic substrate the buffer layers have to transfer the textured structure of the substrate onto the YBCO
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