The Investigation On Rapid-Pyrolysis-Process Of High Performance YBa₂Cu₃o_7-? Superconducting Thin Films Prepared By Chemical Solution Method

The YBa₂Cu₃O_7-??YBCO?coated conductors which showing excellent current carrying characteristics in magnetic field and mechanical properties have wide application prospects in power,transportation,military,medical and other fields.In recent years,chemical solution method?CSD?has attracted much attention for its advantages of no vacuum equipment,low cost,simple operation and the ability to prepare high performance YBCO films.The large-scale industrial production of YBCO coated conductors prepared by chemical solution method is limited by the slow pyrolysis rate during the preparation of YBCO superconducting films.High quality YBCO films require that there is flat,crack-free and wrinkle-free surface on the precursor film after pyrolysis.In order to obtain flat and defect-free precursor films by traditional chemical solution method,the pyrolysis process usually takes more than 10 hours,which is not conducive to the industrialized production of YBCO films by chemical solution method.At present,the critical current density J_c?77 K,0T?of YBCO thin films prepared by fluorine-free chemical solution method is generally about 1 MA/cm²,which is significantly lower than that prepared by slow pyrolysis process.Therefore,in order to enhance the J_c of YBCO thin films,it is very important to study the fast pyrolysis process of YBCO thin films prepared by fluorine-free chemical solution method.Based on the fluorine-free polymer-assisted chemical solution deposition?PA-CSD?method developed by our research group,the process parameters of the precursor film were studied,including the drying temperature and time,heating rate,oxygen flow rate and water bath temperature.The relationship between the above parameters and the structure and properties of YBCO amorphous precursor film and quasi-single crystal film was summarized.And the formation mechanism of precursor film prepared by rapid pyrolysis and epitaxy mechanism of high performance crystalline film were preliminarily discussed..The optimum technological parameters are as follows:drying process parameters are kept at 135?for25 min.And rapid pyrolysis process is heating up to 480?at 15?/min,oxygen flow rate is 500 ml/min,water bath temperature is 15?.The pyrolysis process takes one twentieth of the traditional decomposition method.In this paper,the surface of YBCO precursor film obtained by fast pyrolysis is not smooth enough,compared with slow pyrolysis.There is not a large number of CuO particles assembled,which improved the composition uniformity of precursor films.Because of the fast pyrolysis rate,the stress concentration inside the film results in the dents and bulges on the surface of the films,and cracks,holes and incomplete growth of c-axis texture on the surface of YBCO film after one hour of crystallization.These defects can be basically eliminated by further prolonging the crystallization time.Finally,YBCO thin films with high c-axis texture and good grain bonding can be obtained,of which T_c is 93.3 K and J_c?77 K,0 T?is as high as 3.1 MA/cm².In addition,Co³⁺doping can improve the smoothness and density of YBCO superconducting thin films based on fast pyrolysis process.And it is expected that YBCO thin films with better properties can be obtained.