The Research Of Bi₂Sr₂CaCu₂O_8+? Superconduting Thin Films Derived By Sol-gel Method

Bi₂Sr₂CaCu₂O_8+??Bi-2212?superconducting thin films are expected to be widely used in microelectronic devices as high quality coated conductors,because their superconducting critical transition temperature T_c is relatively high,they don't contain rare earth elements and are insensitive to oxygen.However,the problems like high surface roughness and long sintering time are general in the current researches of Bi-2212 superconducting thin films,which seriously restricts the practical application of Bi-2212 superconducting thin films.Therefore,the preparation of Bi-2212 thin films with uniform density,smooth surface and excellent performance is the goal pursued by researchers.In this study,the formation of Bi-2212 thin films drived by sol-gel method was studied with the non-toxic and economical metal acetate as the starting materials.Based on this,the heat treatment parameters were constantly optimized in order to obtain high-quality single-phase Bi-2212 thin films.Bi-2212 gel thin films were prepared on LaAlO₃?LAO?single-crystal substrates by a dip-coating method using bismuth,strontium,calcium,copper acetates as starting materials,acrylic acid as additives and anhydrous methanol as solvent to explore the reaction process of precursor films.The result showed that in the growth of Bi-2212 thin film,it has undergone three stages of material changes,the decomposition of metal acetates to form corresponding oxides and carbonates,the synthesis of multi-component metal oxides and intermediate phase Bi2Sr2CuO6+??Bi-2201?,and the final formation of Bi-2212 phase with the increasing temperature.The two-step heat treatment process was developed to explore the optimal phase temperature of pure Bi-2212.The gel films were prepared using solution with a total ion concentration of 0.53 moI/L,and then fired at 120 ? for 10 min.After that,the samples were heated at 600 ? for 60 min,secondly were heated to 780 ? at rapid rate for 100 min,and with the introduction of mixed nitrogen and oxygen atmosphere?P?O2?was 1002.9 Pa?,the Bi-2212 thin films with preferred c-axis orientation were successfully prepared,the T_c is 82 K and ?T_c is 5K.The heat-treatment parameters,such as atmosphere,sintering temperature,and holding time were further studied in detail.The surface roughness of Bi-2212 superconducting thin films are successfully controlled at 1?2 nm by continuously optimizing the heat-treatment process,and the whole process was shortened to less than 6 h,T_c is as high as 86 K,?T_c,is as low as 4.3 K,meeting domestic and international advanced level.What's more,the optimal phase area of the single-phase Bi-2212 film is 780 ?/100 min?820 ?/50 min.