Study On Preparation And Properties Of YBCO By Sol - Gel Method

In my work, citric acid, stearic acid, EDTA, DTPA and gluconic acid were added as complexing agent, which had been used for the sol-gel method to prepare the amorphous YBCO xerogel. The YBCO powders and polycrystalline targets were synthesized and compared, then the citric acid has been confirmed as the best complexing agent for YBCO system based on the results. The pure phase Y123 powders could be obtained by calcining xerogel at 750℃, and the powders began melt when the calcination temperature was above 930℃. So the range of powders’ calcination temperature was 750-930℃. The XRD spectra of the powders were compared and showed that lower reaction temperature was not good for the movement of oxygen into Y123 crystal structure. Therefore the square structure would be the main structure of YBa2Cu3O6 in this moment. When the reaction temperature became higher, the oxygen could easy move into the crystal structure and lead it become to orthogonal structure, which show the superconductivity.The results of experiment proved that YBCO material was very sensitive to the oxygen content. So, before the sample melt, the higher calcination and sintering temperature can improve the electrical properties of polycrystalline target.It was found that c-axis orientated ceramics were obtained only when the powders were calcined at 930℃ and sintered at 950℃. YBa2Cu3O7 bulks with c-axis preferred orientation were synthesized by sol-gel method for the first time. It is low cost and the sample is easy to prepare. Below the samples’ melt point, the higher temperature leads to c-axis preferred orientation growth, and the longer sintering time can help to enhance this tendency. The platelike grains and layered structure surface were found in the ceramics. And the samples show good superconductivity.The Y358 xerogel were reacted in air at 840℃ for 12 h, and the samples were synthesized at 890-920℃ for 24 h in an oxygen atmosphere. Then the samples were cooled to 500℃ and retained in oxygen flow for 10 h. In the experiment of synthesizing Y358 by sol-gel method, the (101) orientated Y358 layer were obtained on the surface of the sample. After indexing the diffraction peaks, the lattice constant were calculated, a=3.882 A,b=3.828 A, c=31.008 A. The values of the lattice parameters are consistent with that reported in literatures. After that, the Y358 targets were used for synthesizing thin film by PLD. We failed to prepare Y358 thin film with c-axis preferred orientation, but the film with a-axis or b-axis preferred orientation were obtained. It’s hard to determine the orientation of the films since the a and b axes have the same lengths for Y358 and Y123.