Single Domain Gdbco Preparation And Physical Properties Of Superconductors

A great of works have been done on the fabrication and applications of the high Tc superconductors.Gd-Ba-Cu-O is one of the most promising materials,which can be widely used for applications such as magnetic bearing,energy storage system,and advance motors and magnets etc. The preparation,microstructure and levitation force of Gd-Ba-Cu-O bulk superconductor have been studied in this paper.Batch production of Gd-Ba-Cu-O single domain bulks have been fabricated in small scale by cold-seeding melt growth process with a box furnace.Through adjusting the heat treatment parameter in the growth process,batch of Gd-Ba-Cu-O single domain bulks can be produced by top seeded melt textured growth(TSMTG) technique in an isothermal condition.Meanwhile the preparation,microstructure and levitation force of the GdBCO bulk superconductor have been studied in this paper.GdBa₂Cu₃O_7-δ(Gd123) and Gd₂BaCuO₅(Gd211) powders were synthesized by the solid state reaction method,and all of them were prepared with several times milling and sintering process.The differential thermal analysis(DTA) and XRD analysis results indicate that the propriety reacting temperature of Gd123 powder is in 940℃,and Gd211 is in 900℃.Temperature is a very important factor to the top seeded melt textured growth method (TSMTG).So we primary investigated the temperature parameters and the addition content of Gd211 phase on the quality of the GdBCO sample bulks.The top seed melt-textured growth process including the heating and cooling rate,the dwelling time at high temperature,the start cooling temperature etc..The experiment results show that single-domain GdBCO bulks can be obtained with some reasonable processing parameters:the heating rate is 200℃/h,the dwelling time is 1-2h, the start cooling temperature is 1040℃,the cooling rate during the GdBCO crystal growth process is less than 1℃/h.Large domain or single domain GdBCO bulk can be synthesized with 0.3mol-0.6mol additions of Gd211 particles.In order-to depress the random nucleation during the preparation of single domain GdBCO superconductor bulks,YBCO material with lower melting temperature(compared with GdBCO) is used to realize this goal.The YBCO material was just pressed on the bottom of the GdBCO bulks in a thin layer.The YBCO layer is able to depress the random nucleation during the preparation of single domain GdBCO superconductor bulks.The microstructure of the GdBCO bulk was observed by the scanning electron microscope.The results show that the microstructure of GdBCO bulks is of highly anisotropy.There are fine Gd211 particles dispersion distributed in the Gd123 crystals.The levitation force of single-domain GdBCO bulk has been studied at liquid nitrogen temperature under zero field cooling condition.It is found that the maximum levitation force of the bulk are increasing first and then decreasing with the increasing of the Gd211 particle additon.The maximum magnetic levitation force was reached 5.64 N.The critical temperature of the sample was reached 91K.