Fabrication And Research Of Bi-axially Textured Buffer Layer Of High Temperature Superconducting Coated Conductors

High temperature superconducting(HTS)coated conductors are of great application prospect in many fields such as electric and energy equipments.The fabrication of biaxially textured buffer layers is one of the core technologies of HTS coated conductors.In order to promote the industrialization and the application of HTS coated conductors,it is essential to propose low-cost methods to fabricate high-quality biaxially textured buffer layers.Currently,Magnesium oxide(MgO)buffer layer fabricated via the ion beam assisted deposition(IBAD)technology has been widely adopted by most of the HTS coated conductor manufacturers worldwide.However,because of the high price of large ion sources,the equipment cost of IBAD system becomes a large proportion of the total cost in HTS coated conductor fabrication,resulting in one of the main barriers for the industrialization progress.In this thesis,most of the studies were carried out by employing a magnetron sputtering system,which is a common apparatus for film deposition with the low-cost advantage.Biaxially textured MgO buffer layers could be deposited using the re-sputtering effect during the magnetron sputtering process.Moreover,the study on MgO buffer layer fabrication via the IBAD technology was also included in this thesis.First,the re-sputtering effect during magnetron sputtering process was systematically investigated.During fabrication of oxide films via the magnetron sputtering,the growing film may be bombarded by energetic particles,which mainly comprise negative oxygen(O-)ions and oxygen(O)atoms.This phenomenon is called the re-sputtering effect.By measuring the spatial profile of MgO film thickness by a surface profile-meter,the deposition area where re-sputtering occurred was located.Assuming that the flux density of energetic particles followed a Gaussian distribution,the divergence angle of the particle flux was estimated according to the film thickness profile.Then two methods,in-situ quartz-crystal film thickness monitor and ex-situ surface profile-meter,were used to detect the relationship of MgO deposition rate and sputtering pressure.The condition under which the re-sputtering effect existed was analyzed,and the influence of re-sputtering effect on MgO deposition rate was discussed.Finally,MgO films were epitaxially deposited on(001)oriented single crystal YSZ to preliminarily study the influence of re-sputtering on film growth.Based on the research stated above,it was found that the energy and collimation of the energetic particles was very similar to those of the assisting ions in IBAD process.On the basis of such a discovery,a new method was proposed to fabricate biaxially textured MgO film by using the energetic particles in the magnetron sputtering process.The new method was named energetic particle self-assist deposition(EPSAD),because ion sources were not required.Then,a series of MgO films were fabricated via the EPSAD method.After the homo-epitaxial MgO deposition,X-ray diffraction(XRD)was utilized to characterize the texture of the EPSAD-MgO films.The influences of film thickness,target inclined angle and substrate-target distance on the film texture were studied.According to the analysis of the experimental results,the mechanism of the biaxial texture formation in EPSAD process was discussed and compared to those of IBAD and inclined substrate deposition(ISD).The study of IBAD-MgO technology was also carried out in this thesis.First,an IBAD equipment,which was designed for the fabrication of IBAD-YSZ films,was modified in order to fabricate IBAD-MgO films.Then,the parameter window suitable for IBAD-MgO fabrication was obtained after commissioning,and IBAD-MgO films with the favorable biaxial texture were fabricated.