Preparation Of Tl-1223 High Temperature Superconducting Films On Different Substrates

The discovery of high-temperature superconductors has raised the working temperature of superconductors from the liquid helium temperature range to the liquid nitrogen temperature range,which has greatly improved the practicality of superconductors.Among various types of high-temperature superconductors,Tl series high-temperature superconductors have some advantages such as high critical transition temperature,high critical current density,low microwave surface resistance and strong resistance to deliquescence,which make them of great application value in the fields of strong and weak electricity.They are a very important research material.At high power,they can be used to make ultra-low-loss electrical devices such as superconducting generators,superconducting transformers and superconducting cables;at low power,they can be used to make high-performance passive and active electronic devices such as superconducting filters,superconducting microstrip resonators,superconducting mixers and superconducting infrared detectors.Among the numerous superconducting phases of Tl-based high-temperature superconductors,the Tl Ba₂Ca₂Cu₃O₉（Tl-1223）superconducting phase is one of the most outstanding physical parameters.A key technology for the application of Tl-1223superconductors in the low power range is the preparation of high quality Tl-1223superconducting films.In this work,different types of substrate materials are selected and the process conditions for the preparation of high quality Tl-1223 superconducting films on their surfaces are investigated in order to meet different application scenarios.The specific research contents and innovations are as follows:1.Investigated how to prepare Ce O₂ buffer layer films and Tl-1223 superconducting films with good performance on the surface of sapphire single crystal substrates.It is difficult to prepare Tl-1223 superconducting films on sapphire substrates,and research in this area is currently very scarce.Firstly,the improvement of the surface morphology of sapphire substrates by annealing treatment was investigated.The changes in the surface of sapphire substrates before and after annealing and their effects on the growth of the buffer layer were determined experimentally;then the growth of the buffer layer under different deposition parameters was studied and an annealing treatment was carried out to obtain the optimum conditions for the growth of the buffer layer on sapphire substrates;Then,the specific problems in the process of preparing Tl-1223 superconducting films on sapphire substrates were discussed,and the heating stage of the rapid heating sintering method proposed by our research group in the early stage was improved and optimised.The appropriate heating rate was determined based on the physical properties of each material,and the previous constant temperature method was adapted according to the formation law of superconducting phases.It was used for the post-annealing process of the precursor film to prepare Tl-1223 superconducting films.The prepared buffer layer and superconducting film were characterised by XRD,SEM and other equipment,and the results showed that the buffer layer has a high c-axis orientation and a smooth surface;the superconducting film has a certain phase purity and a clear layer structure on the surface;the superconductivity is good,with a measured critical transition temperature of about 111K and a critical current density of about 1.3MA/cm²（77K,0T）.2.A Hastelloy alloy substrate pre-treatment method is proposed to address the problem of difficulty in directly producing pure c-axis oriented buffer layer films on textureless Hastelloy alloy substrates.In this method,the Hastelloy alloy substrate is annealed in a high temperature environment to achieve uniform oxidation on its surface.The effect of annealing pre-treatment of the Hastelloy alloy substrate with different annealing parameters on the formation of buffer layer films on its surface was investigated.The prepared buffer layer and the surface of the Hastelloy alloy substrate after annealing were characterised using XRD and XPS equipment.The XPS scanning results showed that after annealing in O₂ under certain conditions,many divalent Ni ions were present on the surface of the Hastelloy alloy substrate,and an increase in the intensity of a certain substrate diffraction peak was observed in the XRD diffraction pattern.After annealing,the Hastelloy alloy substrate can easily prepare c-axis oriented buffer layer films on its surface,which provides a good basis for the subsequent preparation of Tl series high-temperature superconducting films.3.Investigations were carried out into the preparation of high quality Tl-1223superconducting films on the surface of lanthanum aluminate single crystal substrates.Improvements and optimisations were made to the heating and constant temperature stages of the rapid heating sintering method.Non-linear heating rates were set based on the physical properties of each material,and a two-stage temperature matching constant temperature method was set based on the formation law of the superconducting phase.This method was comprehensively applied to the precursor film annealing process to prepare Tl-1223superconducting films.After using the improved rapid heating sintering method,Tl-1223superconducting films with good crystallisation,single orientation,dense surface and excellent performance can be prepared on lanthanum aluminate substrates.The critical transition temperature was measured to be about 115K,and the critical current density was about2.2MA/cm².