Research On The Effect Of Strain And Carbon Content On The Properties Of Bi2212 Superconducting Thin Films

Bi-based material has been considered to be one of the most popularunique high-temperature superconductors.Due to it’s unique properties such as short coherence length,strong anisotropy and two-dimensional characteristics,which makes Bi-based material has potential application value in strong and weak electrical fields of superconducting equipments.Stress-strain caused by the mismatch between the film and substrate and the residual carbon content of the film have noticeable effect on the film properties of Bi-based thin film fabricated by sol-gel method.In this paper,the effects of the strain and carbon content of Bi2212 film fabricated by Pechini sol-gel method on the film properties were studied.The main contents and resuts of thesis work are as follows:The lattice constants of Bi2212 films are calculated by using different X-ray Four Circle Diffraction method.The result reveals that using（00l）plane calculation is more authentic campared with non-（00l）plane calculation.The lattice constants of Bi2212 films deposited on the three different kinds substrates is:a,b lattic constant both becomes larger,c lattic constant becomes smaller.So there exists tensile stress within in a-b plane.Using The Williamson-Hall calculated strain,the T_c,onset of thin film showed a trend of initial increased and then decrease in value with the increase of average strain.When The average strain was measured 7.433×10-4,the T_c,onset value rose to 96K.The residual carbon contents were decreased by changing the composition of complexing（using EDTA-CA bi-components complexing agent）in Bi-based superconducting thin film.The EDTA-CA complexing agent ratio of 5:2 was determined and nominal carbon reduction by 9.1%was calculation.The sintering condition was determined by analyzing sintering process of EDTA and EDTA-CA gel using TG-DSC-MS.The result of X-ray diffraction show that non hybrid phase and other oriented grains has been observed,and grain size becomes large and crystallinity is better.The carbon content of EDTA-CA and EDTA films was 15.60%and 17.09%by the electron probe,and the actual carbon content reduced 8.7%.With a decrease of the carbon content in the film,thin film surface roughness become smaller by AFM;the four probe method for the determination of the electrical properties of the film,T_c,onset increased slightly,Tc,zero is obviously improved and △T_c becomes smaller.Among the best electrical properties of the sample T_c,onset,T_c,zero,△T_c and Jc in 80K were 95.23K,84.64K,10.59K and 5.489×10³ A/cm²,respectively.