Research On The Preparation Of Single-domain GdBCO Superconducting Bulk Material By RE+011 TSIG Method

Since the discovery of superconductor and superconductivity in 1911,it has been one of the focuses of experimental scientists and theoretical physicists.Single-domain REBCO(where RE is a rare earth element such as Y,Gd,Sm,Nd,or Yb)superconductors can be used in superconducting magnets,magnetic levitation vehicles,superconducting motors,superconducting filters,flywheel energy storage systems,electromagnetic measurement,et.al.,because of their high superconducting critical temperature(Tc>90 K),strong trapped magnetic flux density,low running costs,and with its special electromagnetic response characteristics.There are broad application prospects and huge potential for REBCO bulk superconductors.Among the many REBCO bulk materials,GdBCO bulk superconductor has the characteristics of high irreversible field of light rare earth superconductors,and there are few substitutions of Gd3+/Ba2+,so it has high superconducting performance and is one of the first hightemperature superconducting materials that are expected to be put into practical use.In this paper,based on the RE+011 TSIG method invented by our laboratory,the optimization of initial powder,the preparation of NdBCO seed crystal,the growth rule and superconductivity properties of single domain GdBCO bulk superconductor are systematically studied.The main work consists of three parts:(1)optimization of preparation method of BaCuO2 precursor powder;(2)study and preparation of NdBCO seed crystal;(3)preparation research of single domain GdBCO bulk superconductors which used RE+011 TSIG method.The main results are summarized as follow:(1)The sintering method for preparing BaCuO2 powder by solid-state reaction is improved.The original three times sintering are all heat treatment at 910?,were optimized into sintering at 895?,905?,and 910? respectively;the results show that this can both ensure the phase purity of the powder,and make the powder easier to be milled and refined.Furthermore,in order to further improve the uniformity and purity of BaCuO2 powder,a method of wet grinding BaCO3 and CuO mixed powder with absolute ethanol and subsequent sintering of the powder is proposed.The original PDF#38-1402 of dry grinding BaCuO2 compared with the FOM value of 3.9,it dropped to 1.3,which provides a guarantee for the preparation of high-quality BaCuO2 powder.(2)Based on the developed BaCuO2 powder,a solid phase source(RE2O3+1.2 BaCuO2,RE=Nd,Gd)for preparing NdBCO crystals and single domain GdBCO superconducting bulk materials and a shared Ybased liquid source(Y2O3+10 BaCuO2+6 CuO);on this basis,using the TSIG method,a well-textured NdBCO crystal was developed,which can be used as a seed crystal for preparing other single-domain REBCO superconducting bulk materials.Using the NdBCO crystal we developed as the seed crystal,using the TSIG method,a single-domain GdBCO superconducting bulk material with good texture and physical properties was developed;the magnetic levitation force density of the GdBCO sample is 10.3 N/cm2(77 K,0.5 T),Higher than the current reported in the literature of the suspension force density of 10.0 N/cm2,9.5 N/cm2 and 8.6 N/cm2.These results show that this method shortens the experimental period,reduces energy consumption,reduces waste water and other pollution emissions,and reduces the cost of preparing NdBCO seed crystals and single domain GdBCO superconducting bulk materials.(3)With BaCuO2 designed and formulated(0.9 Nd2O3+2.4 BaCuO2+CuO)as the initial powder,using TSMG method,an NdBCO seed crystal that can be used to prepare other single domain REBCO superconducting bulk materials was developed.At the same time,using the NdBCO crystal developed by this method as the seed crystal,using the TSIG method,a single-domain GdBCO superconducting bulk material with good texture and physical properties has also been developed.These results show that this is a low-cost and efficient method for preparing NdBCO seed crystals and high-quality single-domain GdBCO bulk superconductors.(4)Used(Gd2O3+1.2 BaCuO2)solid phase source and(Y2O3+10 BaCuO2+6 CuO)liquid phase source,the phase transition and formation temperature of the corresponding compounds were studied by DTA method,and it was preliminarily determined that 900? for 10 h proceed to make the solid phase source generate fine Gd211 phase and the growth temperature of GdBCO crystal.Using the RE+011 TSIG method,a series of GdBCO bulk materials were obtained by quenching at different degrees of subcooling.The size of single-domain GdBCO crystals induced by seed crystals on the surface of the sample was observed,and random nucleation growth appeared on the sample surface in the case of GdBCO crystal,the growth window of single domain GdBCO crystal is determined to be 1018?1042?.These key temperature parameters are of great significance for the preparation of single-domain GdBCO crystals.On this basis,the 020 mm single-domain GdBCO superconducting bulk material has a magnetic levitation force of 36.7 N(77 K,0.5 T).(5)Through the method of doping 1 wt%CeO2,Ni2O3,as well simultaneous doping Ni2O3 and 1 wt%CeO2 in the solid phase source,the influence of Ni2O3 and CeO2 on the morphology and superconductivity of single domain GdBCO samples prepared by RE+011 TSIG method were studied.The results show that the sample doped with 1 wt%CeO2 grows into a single-domain GdBCO crystal with good morphology under the induction of the NdBCO seed crystal.The maximum superconducting magnetic levitation force of the ?20 mm single-domain GdBCO sample is 48.75 N(77 K,0.5 T),Which is significantly higher than the maximum magnetic levitation force of the undoped single domain sample of 38.52 N(77 K,0.5 T).The doping amount of Ni2O3 has a significant effect on the morphology and superconducting properties of the GdBCO sample.When the doping amount of Ni2O3 is less than 2 wt%,the GdBCO sample can grow with a good single domain GdBCO morphology under the induction of the NdBCO seed crystal;when the doping amount of Ni2O3 is greater than 2 wt%but less than 4 wt%,there are different degrees of random nucleation growth regions at the edge of the GdBCO sample;when the doping amount of Ni2O3 is greater than or equal to 4 wt%,the inducing effect of NdBCO seed crystals is no longer obvious,and the entire surface of the GdBCO sample is almost all polycrystals grown by random nucleation.In terms of performance,with the increase of Ni2O3 doping,the superconducting magnetic levitation force of the GdBCO sample shows a significant downward trend.When the Ni2O3 doping amount is 0.15 wt%,the maximum magnetic levitation force of the sample drops to 29.10 N(77 K,0.5 T);when Ni2O3 is doped When the impurity is greater than or equal to 1 wt%,the maximum magnetic levitation force of the sample is only about 1 N(77 K,0.5 T);this is mainly because after Ni2O3 is doped,part of the Ni3+replaces the Cu2+ ions in the GdBCO crystal,resulting in the crystal of the GdBCO crystal.The lattice structure and electronic structure have changed,and this change becomes more and more significant with the increase of Ni2O3 doping,which leads to a sharp drop in sample Tc and superconducting magnetic levitation force.These results show that when the doping amount of Ni2O3 is large,the superconductivity of the GdBCO crystal can only be reduced;if we want to improve the performance of the sample by doping Ni2O3,we must use a smaller doping amount of Ni2O3.