Preparation Of Tl-2223 Superconducting Films By The New Rapid Sintering Process

Superconducting films have excellent electrical properties,low microwave surface resistance and other advantages.The microwave devices prepared by superconducting films have the advantages of small size,easy integration,and low losses,which is an ideal material for manufacturing mobile communication systems.Especially the Tl₂Ba₂Ca₂Cu₃O₁₀（Tl-2223）superconducting film,with high critical transition temperature and strong current transport ability in the ab plane under a strong magnetic field,is a fundamental material for the development of high-performance high-frequency superconducting electronic devices and power electronic devices.The single crystal such as lanthanum aluminate and sapphire have less uneven strain and defects,and their atomic arrangement is highly regular and symmetrical,which can be used as the substrate materials for growing high-temperature superconducting films;Hastelloy alloy has high corrosion resistance,toughness and oxidation resistance,and can be used to prepare Tl-based high-temperature superconductive strips.However,it is difficult to grow high-quality Tl-2223 superconducting films on the surfaces of the above three substrates,so there are relatively few research and application reports on them.This article focuses on the preparation of high-quality Tl-2223 superconducting films on lanthanum aluminate and sapphire substrates through optimized sintering processes,and the preparation of CeO₂films on the strips surface of Hastelloy alloy,providing a good foundation for the subsequent preparation of superconducting films.The work done in this article is as follows:（1）Tl-2223 superconducting films were prepared on（00l）oriented lanthanum aluminate substrate by the new rapid sintering process,and the effects of sintering temperature and time at high temperature on the crystal structure,surface morphology and superconducting properties of the superconducting films were explored in the oxygen environment.The XRD results indicate that the sintering temperature and time are crucial for the grain orientation of Tl-based superconducting films.By using appropriate sintering temperature and time,pure c-axis oriented Tl-2223 films can be prepared with good crystal quality.SEM shows that the superconducting film has a smooth surface,dense crystal structure and obvious layered growth structure.The Tl-2223 film has excellent superconducting properties,with the critical transition temperature of115K and the critical current density（77K,0T）of 1.6MA/cm².The process simplifies the preparation process of Tl-2223 superconducting films and effectively improves experimental efficiency.By exploring the preparation of pellets and the sintering conditions of precursor films,the technological conditions such as the ratio of pellets,sintering atmosphere and heating rate required for the growth of pure phase Tl-2223 superconducting film were mastered.（2）The changes in grain structure and surface morphology of sapphire substrate after annealing,as well as the optimum thickness and sputtering process of preparing the CeO₂buffer layer on the surface were studied.The test results show that the diffraction peak intensity of the annealed substrate increases,the half-height width decreases to 0.07°,the surface flatness increases,and the wide step structure appears.After annealing,the root mean square roughness of the substrate is reduced to 0.205nm,the step height is about 0.35nm,and the width is 135nm.After changing the sputtering power,temperature,and time in the experiment,the prepared films were all grown in pure c-axis orientation.When the sputtering conditions were600℃120W1Pa5min,the obtained CeO₂film had good grain orientation consistency,and the full-width half-maximum value of the（002）diffraction peak was only 1.34°.（3）The effect of sintering temperature at high-temperature section on Tl-2223superconducting film in the new rapid sintering process on the sapphire substrate was studied.With the increase of temperature,the mixed growth of Tl-2212 phase and Tl-2223 phase transforms into the main phase of Tl-2223 phase.After the temperature continues to increase,the Tl-2223 phase shows a poor consistency of pure c-axis orientation.But including grains with orientations such as（112）and（116）,and the sample has a high resistance at room temperature,which may be related to the thallium content of the pellets and sintering time.At present,the growth of Tl-2223 superconducting films on the sapphire substrate is still in progress.（4）The effect of Hastelloy alloy strip annealing in different atmospheres on the grain orientation of CeO₂films was studied.The XPS results indicate that a large amount of Ni O is generated on the strip surface annealed in an oxygen atmosphere,and the Ni O crystal structure provides an epitaxial template for the growth of CeO₂films.The experiment found that the optimal annealing condition for the strip was 850℃for 5 minutes.The results show that the strip annealed in N₂can induce the growth of CeO₂films along the c-axis direction to a certain extent,but the consistency of c-axis orientation is not high.However,the strip annealed in the argon-hydrogen mixture did not generate Ni O on the surface,so the CeO₂films grew in the（111）orientation.（5）The optimal sputtering process for growing CeO₂films on Hastelloy alloy strip was systematically investigated.XRD tests showed that CeO₂films prepared by RF magnetron sputtering are sensitive to sputtering parameters,and when the temperature was too high（>700°C）or too low（<640°C）,the power was too high（>100W）or too low（<40W）,and the air pressure was too high（>3Pa）,the CeO₂diffraction peaks with orientations such as（111）and（311）appear in the films.The experimental results show that the best sputtering condition is 680℃80W2Pa1h.