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Biaxially textured -oriented SrTiO3 films were solution deposited on LaAlO3 single crystals and -oriented polycrystalline Ni tapes. Solution variables including varying titanium alkoxide chain length, inclusion of chelating agents, and inclusion of donor dopant, were investigated for their effect on film orientation, morphology, and oxygen diffusivity. The best SrTiO3 orientation on high lattice mismatch (11%) Ni substrates was achieved through use of a discontinuous nucleation seed layer, which provided nucleation sites for subsequent continuous SrTiO3 films. Increased titanium alkoxide chain lengths appeared to suppress titanium hydrolysis reactions and improve film orientation. 13C nuclear magnetic resonance showed that significant quantities of water were generated due to esterification reactions, which appeared to cause hydrolysis and subsequent orientation degradation in the absence of chelating agents such as acetylacetone.

I. INTRODUCTION

YBa2Cu3O7−␦ (YBCO) based coated conductor wires have sparked widespread interest,1–3 with near-term applications in prototype high-efficiency power transmission, power storage, transformers, high field magnets, and motor systems.4 Implementation of these high current and/or high magnetic field applications would be enabled by a cost-effective route to a high critical current density (Jc) superconducting wire structure, such as caxis-oriented YBCO thin films on inexpensive base metal tape substrates.5 However, material processing issues remain critical since avoiding nonstoichiometry, out of plane misorientation, and grain-to-grain misorientation is necessary to obtain YBCO film superconducting Jc (77 K) > 1 MA/cm2.1–3,6–8 Deposition of YBCO on oxide-buffered, rolling-assisted biaxially (in-plane) textured (RABiT) Ni substrates is one promising approach to these issues.5 RABiT substrates are currently in production by several commercial groups in long lengths and consistently provide a biaxial -oriented growth surface with 5–9° grain-to-grain alignment, and rootmean-square (rms) surface roughness 1 MA/cm2) YBCO film on top. This research addresses the issues of CSD SrTiO3 phase evolution, biaxial orientation, oxygen diffusivity, and compatibility with Ni and YBCO via a CSD route. A

J. Mater. Res., Vol. 17, No. 7, Jul 2002 Downloaded: 11 Mar 2015

IP address: 169.233.226.23

J.T. Dawley et al.: Chemical solution deposition of -oriented SrTiO3 buffer layers on Ni substrates

metal alkoxide/metal acetate-based CSD process was used to fabricate SrTiO3 on RABiT Ni substrates, with a focus on the influence of ligand chemistry, doping, and esterification reactions on the fabrication of welloriented films.23–25 Studies suggest that well-oriented SrTiO3 (STO) films would be effective as oxygen barriers26 and would be compatible with Ni and YBCO for wire applications. II. EXPERIMENTAL PROCEDURE

RABiT Ni substrates with a nominal orientation were supplied by Oxford Superconducting Technologies. The as-received 75-␮m-thick Ni tape was preannealed under flowing dry 3% H2/N2 at 1100

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