Research On The Effect Of Strain And Sol System On The Superconducting Properties Of Bi2212 Thin Films

Bi-based high-temperature superconducting materials have attracted widespread attention in the scientific community due to their short coherence length and strong anisotropy.Especially,superconducting microwave devices and intrinsic Josephson devices which developed based on characteristics such as low surface microwave resistance and intrinsic Josephson junction,have broad prospects.In this paper,the effects of strain and sol system on the superconducting properties of Bi2212 thin film fabricated by Pechini sol-gel method are studied.The specific works are as follows:The thickness of Bi2212 thin films were fabricated by different spinning speeds and different spinning times.And the lattice constant of the Bi2212 thin film of different thickness was calculated by X-ray four-circle diffractometer.The lattice constant of Bi2212 thin films was analyzed,and the mismatch strain between the film and the substrate was studied,as well as the relationship between the film thickness and the mismatch strain.It is found that the tensile stress in the a-b plane of the Bi2212 thin films on the SrTiO3(100)single crystal substrate has a lattice constant a/b greater than the a/b value of the intrinsic Bi2212 crystal.As the thickness increases,the mismatch strain of the film gradually decreases,the superconducting critical transition temperature of the films gradually increases,and the superconducting transition width gradually decreases.The thickness of the most spinning times films is the largest,which is 126.02 nm,and the surface mismatch strain is the smallest,which is 2.423 ×10-3.And the superconducting critical transition temperature is the highest,which is 96.38 K.By changing the complexing agent,that is,using tartaric acid as a complexing agent to reduce the carbon content in the precursor sol,thereby improving the surface morphology and superconducting properties of the Bi2212 films.By studying the surface morphology of Bi2212 thin films fabricated by different spinning processes.It was found that the surface morphology of the Bi2212 thin film fabricated on the SrTiO3 single crystal substrate which heat-treated at 500? for 5 min was superior to the surface morphology of the thin film fabricated on a SrTiO3 single crystal substrate which coated active agent aqueous solution And the best thin film had a surface roughness of only 11.056 nm.Through the optimization of the sintering process,it was found that Bi2212 thin film fabricated from a sol using tartaric acid as a complexing agent can fabricate a film with high phase purity in the temperature range of 822-825?,and the sintering time is preferably 3035 min.Through analysis of phase composition and electrical properties,it was found that when the molar ratio of total metal ion to tartaric acid is 1:1,the fabricated Bi2212 film has higher phase purity.And its superconducting transition temperature is 91.73 K,and superconducting transition width is only 9.79 K,which shows satisfactory superconducting performance.The success of the fabrication of Bi2212 thin film using tartaric acid as a complexing agent shows that this method is very promising in improving the surface morphology and improving the electrical properties of the thin films.