Research On Preparation Of Biaxially Textured Double-sided Y(Gd)BCO Coated Conductor By MOCVD

YBCO high temperature superconducting coated conductors(or YBCO tapes)exhibit strong current-carrying capability,excellent mechanical strength,and remarkable in-field performance,and therefore have great application value in the field of high-power electricity.Currently YBCO tapes have been applied in many devices successfully,such as electric power cable,fault current limiter,large magnet and wind power generator.However,it is still a challenge to optimize the structure and performance of YBCO tapes further.In this paper,the preparation process of double-sided Y(Gd)BCO tapes was investigated based on an improved metal organic chemical vapor deposition(MOCVD)systems.The main research contents are as follows:1.Improvement of the electric heating device:Firstly,by mechanical analysis of the contacts between the substrate edge and electric brush,the influence of the substrate thickness on electrical stability was investigated.Secondly,the heating device was redesigned to ensure a more stable contact than before.Moreover,a pulley group is used to prevent the tapes from slipping in the horizontal direction.At last,100?m and 62?m template substrates were used to prepare Y(Gd)BCO films for comparison.The engineering critical current density(J_e)at 0 T and 77 K by using 62?m substrate reaches 101 A/mm²,which is twice as high as the former.2.Research on the preparation process of Y(Gd)BCO superconducting films:A moderate high deposition rate can eliminate the CuYO₂ precipitates in the films,improve the structure and increase the critical current density(J_c).Low heating current will lead to the formation of Cu-rich precipitations and a-axis grains.As the current increases,the Cu-rich precipitations reduce and the a-axis grains disappear.However,when the heating current is too high,precipitations will appear in the films again.A lower Cu ratio leads to the formation of pores in the Y(Gd)BCO films,which makes a less J_c;Increasing of Cu ratio can eliminate the pores,but it leads to Cu-rich precipitates in the films.Under the condition that the molar ratio of Y\Gd\Ba\Cu is0.8\0.8\2.8\3.3,the deposition rate and heating current are 520 nm/min and 23.7A,respectively,the Y(Gd)BCO films are flat and dense without precipitates.The values of FWHM of out-of-plane texture and in-plane texture are 1.44° and 2.58°,respectively.And the J_c value can reach 4.5 MA/cm².3.Research on high J_e double-sided Y(Gd)BCO tapes:Firstly,the preparation process of double-sided Y(Gd)BCO tapes was investigated based on a double shower design.Secondly,by using a multiple-layer Y(Gd)BCO structure,the problems of rough surface and low performance that often occurred in thick films were solved.Finally,multiple-layer Y(Gd)BCO films were prepared on the basis of double-sided Y(Gd)BCO films to improve the J_e of Y(Gd)BCO tapes.The J_e of 250 nm double-sided Y(Gd)BCO tapes reaches 342 A/mm².With the multiple-layer structure,the FWHM values of out-of-plane texture of double-sided 1?m Y(Gd)BCO thick films are optimized to a better level of less than 1°;the FWHM values of in-plane texture are less than 2.3°;and the J_e of the Y(Gd)BCO tapes reaches 900 A/mm² from342 A/mm².