Preparation And Properties Of Bi₂Sr₂Ca₂Cu₃O_10+δ Superconducting Thin Films By Sol-gel Method

Bi2Sr2Ca2Cu3O10+δ(Bi-2223)superconducting thin films are widely used in coating conductors due to high superconducting critical transition temperature(Tc)free of rare earth elements and stability on exposuer to air.However,due to the complex structure of Bi-2223 phase and the narrow temperature range of the phase,the current research generally has the problems of complicated preparation process,harsh conditions and long preparation cycle,which seriously limits the practical application of Bi-2223 thin film.Therefore,the preparation of Bi-2223 films with high purity high quality and excellent performance has important research and application value.In this paper,metal acetate as raw material,acrylic acid as additive and anhydrous methanol as solvent,the sol-gel method was used for obtaining Bi-2223 sol with good film forming and stable performance by adjusting the sol ratio and continuously optimizing the formulation.Subsequently,the Bi-2223 gel film was prepared on the LaAlO3(LAO)single crystal substrate by dipping and pulling method,and the phase evolution process of Bi-2223 thin film was studied.It was found that the metal acetate was decomposed to form respective metal oxides and carbonates,then formed multi-component metal oxides and intermediate phases Bi2Sr2CuO6+δ(Bi-2201)and Bi2Sr2CaCu2O8+δ(Bi-2212),finally formed the Bi-2223 phase at high temperature.When the sol ratio is Bi:Sr:Ca:Cu=2.2:2:2:3,the film was heat-treated at 860℃ for 120 min under N2:O2=96:4 atmosphere,Bi-2223 film with a relative content of 69.8%in Bi-2223 phase can be obtained.In order to improve the purity of Bi-2223 phase,(Bi,Pb)-2223 thin film doped with Pb was prepared,the effects of Pb element doping amount,heating rate during heat treatment,heat treatment temperature,heat treatment time,heat treatment atmosphere and other factors on the film quality were studied.When the ratio of the sol is Bi:Pb:Sr:Ca:Cu=2:0.2:2:2:3,the film was heat-treated at 850℃ for 120 min at N2:O2=96:4 atmosphere.(Bi,Pb)-2223 was successfully prepared,with c-axis epitaxial growth and phase purity of 87.8%.Tc as high as 101.5 K and theΔT as low as 7.5 K.