ИСТИНА

Oxide compounds with pyrochlore or fluorite structure, La2Zr2O7 and La2Hf2O7, are promising materials for catalytic, optical and electrical applications. Moreover, due to their low lattice mismatch with the YBa2Cu3O7-x high temperature superconductor (~1%) they can be good buffer layers in the architecture of high temperature superconducting tapes [1]. The aim of this work was to develop chemical solution deposition processes to grow La2Zr2O7 and La2Hf2O7 thin films on biaxially textured <001>(001) metal alloy substrates. The coating solutions consisted of a stoichiometric mixture of lanthanum oxide and zirconium or hafnium acetylacetonates dissolved in propionic acid. The advantages of those solutions were their stability at high concentrations and excellent wetting behaviour at metal substrate surfaces. The chemistry of the precursor solutions was studied using thermogravimetric analysis and infrared and NMR spectroscopy. The formation of heteroligand metal carboxylates was found in these complex solutions. The next step was to study the dip coating process of the oxide precursor layer onto continuously moving 80 micron thick Ni-W alloy tapes. There are several important parameters influencing the oxide films thickness and uniformity, namely the solution concentration, viscosity, temperature and speed of tape motion through the solution bath. We quantitatively studied the dependence of the film thickness on the solution concentration and the tape motion rate and found it to correlate well with the predictions of the Landau-Levich theory [2]. Crystalline oxide films of La2Zr2O7 and La2Hf2O7 on the Ni-W tapes up to 10 m long were obtained via high temperature treatment (1000-1150oC) of the precursor-coated tapes under reducing atmosphere in the reel-to reel tape motion mode. X-ray diffraction (θ-2θ, ω- and φ-scanning), scanning electron microscopy and electron backscattering diffraction were used for characterization of oxide films. Using the solution deposition approach described we succeeded in preparing biaxially textured La2Zr2O7 and La2Hf2O7 films. The tapes with the La2Zr2O7 films were subsequently used as single buffer layers to make coated conductor tapes with simplified architecture YBa2Cu3O7-x/La2Zr2O7/Ni-5W and YBa2Cu3O7-x/Y2O3/La2Zr2O7/Ni-5W. The superconducting critical current 150 A/cm was measured in the conductors. [1] K. Knoth, R. Hühne, and S. Oswald, Thin Sol. Films 2008, 516, 2099-2108. [2] L. Landau, V. Levich, Acta Phisicochim USSR 1942, 17, 42. Acknowledgements This work was supported by the Russian Foundation for Basic Research grants No. 12-03-00754-a and № 14 03 32063.