Preparation Of Second-generation High-temperature Superconducting YBa₂Cu₃O_7-x Thin Film And Buffer Layer Film

The high-temperature superconductor YBa₂Cu₃O_7-x?YBCO?has been paid much attention due to its high electrical performance.YBCO was made into tape generally for various applications.For YBCO wire preparation,buffer layer films and YBCO film have to be grown on flexible metallic tape.At present,there are many methods to prepare buffer layer films and YBCO film.Among these techniques,MOCVD has been considered as one of the most potential approaches due to its advantages of uniform coverage,high controllability for film composition,large area coating for substrate with complex shape and relatively high deposition rate.Laser chemical vapor deposition,termed LCVD,is a special MOCVD technique which is enhanced by a continuous laser beam.LCVD is able to quicken its deposition process,strengthen film's preferred orientation and reduce corresponding deposition temperature.In contrast to conventional MOCVD,the laser CVD could be a more promising method in preparing YBCO film.In this paper,we firstly prepared high quality CeO₂ buffer layer films on?100?oriented LaAlO₃ single crystal substrate by LCVD using solid precursor.Then,we synthesized high quality YBCO films on Hastelloy C276 substrate by spray atomizing and coprecipitating LCVD.In the present study,we investigated the effects of laser power?deposition temperature?and deposition rate on the performance of CeO₂ and YBCO film.For CeO₂ films preparation,we chose?100?LaAlO₃ single crystal for substrate,films were prepared at deposition temperature ranged from 947 to 1096 K?corresponding laser power was from 52 to 185 W?by laser chemical vapor deposition.At deposition temperature of 1027-1096 K?laser power was from 115 to 185 W?,highly?100?-oriented CeO₂ films with wedge-caped columnar grains were prepared,whose epitaxial growth relationship was CeO₂[100]//LAO[100]?CeO2[010]//LAO[011]?.Their full width at half maximum of the?-scan on the?200?reflection and that of the?-scan on the?220?reflection were 0.8-1.8°and 0.7-1.2°.In the present study,the highest deposition rate of CeO₂ film was 32?m/h,but the film did not show pure?100?orientation,the highest deposition rate of CeO₂ film with pure?100?preferred orientation was 30?m/h.For YBCO films preparation,we chose Hastelloy C276 for substrate,films were prepared at deposition rates ranging from 10 to 55?m/h by laser chemical vapor deposition.At a deposition rate of 10?m/h,c-axis-oriented YBCO film with high critical temperature?T_C?of 91 K and critical current density?J_C?of 2.4 MA/cm² was prepared,which showed an epitaxial growth mode of YBCO[001]//CeO₂[100]?YBCO[100]//CeO₂[011]?.The full width at half maximum?FWHM?value of the?-scan and that of the?-scan of the sample were 1.9°and 3.2°.At a deposition rate of 45?m/h,a-axis-oriented YBCO film was prepared,whose T_C and J_C were 78 K and 0.4 MA/cm².The YBCO film showed an epitaxial growth mode of YBCO[100]//CeO₂[100]?YBCO[001]//CeO₂[011]?.FWHM value of the?-scan and that of the?-scan of the sample were 4.9°and 9.5°.