High Performance REBCO Bulks Composited By Refined RE211 Particles Derived From Homogeneous Nucleation Catastrophe

High-temperature superconductor(HTS)bulks of REBa2Cu3O7-?(REBCO or RE123,RE=Y,Sm,Nd)materials,possessing high critical current density(Jc)and high trapped magnetic field,have attracted a significant amount of attention,owing to their potentials for device applications,such as hysteresis motors and magnetic bearings.As is well known,the superconducting performance of HTS depends strongly on their microstructure.Particularly,Jc,a key parameter for superconducting properties,is proportional to the number of the nanoscale defects,i.e.pinning centers per unit volume in REBCO bulks.As is known,the interface of the nonsuperconducting phase RE2BaCuO5(RE211)and the superconducting phase RE 123 can be considered as pinning centers.Therefore,the refinement of RE211 particles is a key challenge for fabricating high performance REBCO bulks.This thesis is mainly focused on two aspects,and the main results are listed below.1.YBa2Cu3O7-? superconductor bulks composited by Y2BaCuO5 nanoparticles derived from homogeneous nucleation catastropheFor the first time,using modified precursor powder(Y211-free),Y2O3+Ba2Cu3Oz,we have succeeded in fabricating Y123 bulks in top-seeded melt-growth(TSMG).Remarkably,compared with the conventional samples,the superconducting properties of the MPP samples are effectively improved due to the refined Y211 particles.More concretely,nano-sized Y211 particles nucleate instantaneously and simultaneously through peritectic solidification of Y2O3+Ba2Cu3Ox?Y211 at a high temperature above Tp.As a result,the average levitation force of the MPP samples is proved to be approximately 10%higher than those of the CPP ones,and the trapped field was increased from 0.418T to 0.636T.Most importantly,the deep understanding of Y211 nucleation and growth related to peritectic reaction in MPP and CPP is universally worthy for the refinement of other RE211.2.High performance SmBCO bulks composited by homogeneous distribution of small-sized Sm211 particlesTo suppress the substitution of Sm3+on Ba2+,powder without pre-existing Sm211 particles,Sm2O3+Ba3Cu4O7 was determined as modified precursor powder with Ba-rich.In addition,to readily achieve the homogeneous distribution of Sm211 particles,the layered MPP with Ba-rich(LB-MPP)was employed to fabricate the SmBCO bulks.Remarkably,optical micrographs and scanning electron micrographs(SEM)confirmed that the dispersion of small-sized Sm211 particles in various locations of the fully-grown sample was quite uniform.Accordingly,the values of levitation force are 18.6N,20.2 N,22N in the case of CPP,MPP,LB-MPP samples.Meanwhile,levitation force of the large size MPP sample was effectively improved to 44N,and higher levitation force will be obtained in the circumstances of the large size LB-MPP sample.In summary,the merit of time and cost-saving in MPP,the scientific understandings of Y211 formation mechanism related to peritectic reaction(Y2O3+BaxCuyOz?Y211),and the new conception of LB-MPP to form uniform distribution of refined Sm211 particles,are universally worthy for batch production of other large size LREBCO bulks.