ИСТИНА

Oxides with pyrochlore or fluorite structure, La2Zr2O7 (LZO) and La2Hf2O7 (LHO), due to their low lattice mismatch with the YBa2Cu3O7-x (YBCO), can be good buffer layers in the high temperature superconducting tapes [1, 2]. The development of simple buffer layer architectures as well as cheap techniques of the deposition is still important tasks for coated conductor technology. By this the aim of the work was to develop chemical solution deposition process to obtain thick <001>(001)-textured La2Zr2O7 and La2Hf2O7 films on metal substrate. The coating solutions consisted of a stoichiometric mixture of lanthanum oxide and zirconium or hafnium acetylacetonates were dissolved in propionic acid. The advantages of those solutions were their stability at high concentrations and excellent wetting behavior on metal substrate surfaces. The chemistry of the precursor solutions was studied using thermogravimetric analysis and infrared and NMR spectroscopy. To obtain smooth LZO/Ni-5W coatings with perfect cubic texture and with very small side effect we’ve developed continuous real to real CSD process using carboxilates, followed with continuous texturing thermal treatment. The film texture quality was shown to be drastically dependent on the residual carbon content which is strong function of the film thickness and thermal treatment regime. Thus, the attempt to get sharply textured LZO films with thickness more than 50-nm (this thickness is not enough to stop diffusion of Ni into superconducting layer) using the only thermal treatment in reducing Ar/H2 atmosphere, recommended in the literature [1, 2], was unsuccessful. For one deposition step obtaining of 200 nm-thick LZO films with sharp biaxial texture we’ve proposed to combine low-temperature (450oC) oxidative treatment with the following high temperature treatment (1150oC) in H2 (pH2= 20-30 mbar). The texture was much improved when the oxidation process was activated with ozone admixture to the furnace atmosphere. The effective carbon elimination at the low temperature oxidative treatment promotes faster diffusion of oxide components at the high temperature texturing annealing, leading to much higher texture and crystallinity. The quality of the buffer layers obtained made possible to realize the simplest 2G HTSC tapes YBCO(CVD)/200 nm LZO(CSD)/Ni-5W with Jc = 1.1 MA/cm2. The XRD, Auger – spectroscopy, EBSD, SEM, TEM and ED techniques were used to characterize buffer layers.