In the context of CSD-MOD growth of coated conductors for low cost and scalable production of YBCO coated conductors, new solutions are proposed in accordance with the new requirements concerning environmental safety and product performance. Looking at these objectives we will present here our work in the preparation of metallorganic precursor solutions with reduced fluorine content, which fulfill the requirements of superconducting YBCO epitaxial layers, leading to high superconducting performance. Solutions with low fluorine precursors with different solvents and amounts of additives have been stabilized and their rheology modified for substrate wettability. Thermal decomposition analysis and infrared spectroscopy performed directly in films, have revealed the different decomposition steps and NMR analysis could unveil the chemical reactions taking place in the solution. Upon optimization of the growth process parameters, T c and J c (77K) of 90 K and 3-4 MA/cm 2 are obtained.

No abstract

The thermal decomposition of several metal organic precursors, used in the preparation of YBa 2 Cu 3 O 7-x superconducting coated conductors (Cu acetate, Cu, Y and Ba trifluoroacetates and Ce propionate) is analyzed by means of several thermoanalytical techniques (TG/DTA, MS and DSC). In all cases, the metal organic precursors deposited as thin films decompose differently than powders from the same precursors. In thin films, decomposition is facilitated by the easier transport of reactive gas from the surrounding atmosphere and by the easier out-diffusion of volatile products. Consequently, films decompose at lower temperature and are more sensitive to the presence of any residual reactive gas in the furnace. Good thermal contact with the substrate is also shown to minimize overheating in films and avoid combustion processes that are otherwise often observed during the thermal decomposition of powders. Finally, the formation and stability of intermediate products towards the oxide formation, such as metal fluorides, differs in films because of the easier gas exchange. With respect to powders, these compounds are much less stable in films, where their decomposition temperature can be lowered by several hundreds of degrees Celsius. While in some cases the behaviour of films can be predicted by analyzing varying masses of precursor powders, this is not always the case. Therefore, thermal analysis carried out on films is recommended to avoid erroneous conclusions about materials preparation drawn from powders.

No abstract

13The thermal decomposition of barium trifluoroacetate thin films under different 14 atmospheres is presented. Thermogravimetry and evolved gas analysis have been used 15 for this in situ analysis. We focus our attention on the different behavior exhibited

13We present the first use of the thermal analysis techniques to study yttrium trifluoroacetate thin 14 films decomposition. In situ analysis was done by means of thermogravimetry, differential 15 thermal analysis, and evolved gas analysis. Solid residues at different stages and the final product 16 have been characterized by X-ray diffraction and scanning electron microscopy. The thermal 17 decomposition of yttrium trifluoroacetate thin films results in the formation of yttria and presents 18 the same succession of intermediates than powder's decomposition, however, yttria and all 19 intermediates but YF 3 appear at significantly lower temperatures. We also observe a dependence 20 on the water partial pressure that was not observed in the decomposition of yttrium 21 trifluoroacetate powders. Finally, a dependence on the substrate chemical composition is 22 discerned. 23 24 25

We have employed the CSD method to synthesize GdBCO and GdBCO-Gd 2 O 3 nanocomposite 250-300 nm thin films. For this we have designed a new Low-Fluorine (LF) solution never used before in the synthesis of GdBCO thin films that allow to reduce the HF release by 80% and increasing the reproducibility of the pyrolysis process. The growth of these thin films required the design of a new thermal process what we called "Flash-Heating" in which the heating rate is extremely fast (~600 ºC/min). The structure and the superconducting properties of the pristine GdBCO films are excellent showing a (00l) epitaxial orientation of the GdBCO grains and T c values that reach 92.8 K which means and enhancement of more than 1 K with respect to the standard YBCO films. The calculated J c inside the grains ( ) present also remarkable values: (5 K) ~ 40 MA/cm 2 and (77 K) ~ 3.3 MA/cm 2 . Finally, the GdBCO-Gd 2 O 3 nanocomposites films, with a 20% mol of Gd 2 O 3 , exhibit superior superconducting properties and pinning performances with respect to the GdBCO pristine films.

No abstract