Optimizing SrTiO 3 films on textured Ni substrates using chemical solution deposition
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T.G. Holesinger Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 20 October 2004; accepted 7 January 2005)
Chemical solution deposition (CSD) is used to grow high-quality (100)-oriented films of SrTiO3 (STO) on CSD Ba0.2 Ca0.8TiO3(100) (BCT) templates on textured W-doped Ni(100) (Ni:W) tape substrates. The BCT template films form a thin layer or “skin” that bridges its significant porosity. STO films grown at 1000 °C appear optimized for heteroepitaxial orientation, surface coverage, and film smoothness. Both interfaces in the STO(100)/BCT(100)/Ni:W(100) stack demonstrate excellent atomic registry and compositional abruptness. Doping STO with a few atomic percent of Nb reduces oxygen diffusion into the film by an order of magnitude and provides greater protection to the Ni interfacial surface from oxidation during the growth of additional functional oxides requiring relatively higher p(O2) high-temperature processing, such as superconducting YBa2Cu3O7−␦. CSD growth of BCT and STO also planarizes pre-existing grooves in the Ni:W(100) tapes while maintaining a high degree of orientation by forming facets at the interfaces.
I. INTRODUCTION
Chemical solution deposition (CSD) was demonstrated recently for all the superconductor and buffer layers needed to fabricate high critical-current density (Jc) coated-conductors on textured Ni(100) tapes.1 Limitations of superconducting properties centered primarily on deficiencies (misorientations, morphology) in the buffer layer. This paper deals with the annealing conditions for CSD Nb-doped SrTiO3 (Nb:STO) films on textured Ni(100) tapes needed to reduce film porosity and improve both orientation and surface morphology. Such improvements lower oxygen diffusion through the buffer layer during YBa2Cu3O7−⭸ (YBCO) overgrowth and create a better template, together resulting in YBCO films with better c-axis orientation than previously reported.1 STO(100) has an excellent lattice match and chemical compatibility with YBCO and is known to support the growth of high-quality superconducting films.2 Growthoriented STO films on both MgO(100) and STO(100) single crystals was first reported in 1989 using sputter deposition at substrate temperatures ∼600 °C. These
a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: Nozomi Photonics, San Jose, CA. DOI: 10.1557/JMR.2005.0137 910
methods were quickly improved; within two years, Josephson junction devices were reported using conducting Nb:STO films sandwiched between two YBCO layers, all deposited by off-axis sputtering at 700 °C onto STO(100) single crystal substrates.3 Sol-gel thin films of polycrystalline STO on fused silica substrates annealed to 550 °C were reported that same year using alkoxide precursors chemically modified by adding chelating agents, which aided in densification.4 High-temperature annealing to 1100–1200 °C resulted in epitaxial CSD films of STO on STO(100) crystals.5 Transparent and crack-free polycrystalline STO films were soon grown, using CSD, onto st
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