Research On The Irradiation Effect Of Bi-2212/YBCO High-temperature Superconducting Materials

As a kind of clean energy which can solve human energy and environment problems,fusion energy has been widely concerned.It is well known that the superconductivity magnet are the basis of the establishment and development of magnetic confinement fusion reactors.When the fusion device works normally,the superconducting material will be irradiated by particles or rays.Therefore,it is very important to evaluate the irradiation effect of superconducting materials.Bi-2212(Bi₂Sr₂Ca Cu₂O_8+?)is the only high-temperature superconducting material that can be made into isotropic round wire(RW).In addition,it has excellent current carrying performance at 4.2 K,which is one of the most promising high-temperature superconducting materials under high field(>20 T).As the first high-temperature superconductor with critical temperature(T_C)over 77 K,YBCO can carry a large critical current under a strong magnetic field of 77 K.Therefore,it is a real superconducting material for strong electric application at liquid nitrogen temperature region.Therefore,the irradiation effect of two kinds of high temperature superconducting materials(Bi-2212 wire and YBCO tape)was studied in this paper.The effects of before and after irradiation on the microstructure,mechanical properties and superconducting properties of high-temperature superconducting material were systematically studied by a series of characterizations,such as:X-ray diffraction(XRD),Scanning electron microscope(SEM),Transmission electron microscope(TEM),Nano-indentation,Physical property measurement system(PPMS).The main results are as follows:(1)The effects of He⁺ion irradiation of Ag-sheathed Bi-2212superconducting round wire were evaluated.Room-temperature XRD profiles shows that all the peaks shifted rightward significantly with broaden(111)_Agpeak,indicating that the high-energy He⁺irradiation resulted in appreciable defects and strain in the superconducting wire.Meanwhile,the in-situ high-temperature XRD tests shows that the lattice constant and the thermal expansion coefficient were deduced in the irradiated sample due to the presence of the generated defects.After irradiation,the grain size of the Ag sheath was refined,and twin morphology changes from flat twin to step twin.Meanwhile,the lattice of Bi-2212 superconductor was distorted obviously,as confirmed by TEM.The I_Cat 4.2 K of the superconducting wires in the field of 0-14 T,determined by PPMS,was decreased substantially after irradiation because of the lattice distortion and the consequently induced strain in the Bi-2212 superconductor.In addition,nano-indentation test results reveal an obvious hardening phenomenon of the irradiated Ag sheath,which was mainly associated with the formation of stepped twins and the refinement of grain size.(2)The effects of D-T fusion neutron irradiation(fluence1.55×10¹³n/cm²and 7.78×10¹³n/cm²)on Bi-2212 wires and YBCO tapes were studied carefully.The results shows that the diffraction peak of Ag sheath in Bi-2212 wire has no obvious change before and after irradiation.Based on TEM results,the microstructure of Ag sheath and Bi-2212superconductor does not change significantly before and after irradiation.The I_Cof the irradiated samples measured by PPMS(4.2 K,12 T)were slightly increased(within the error of range)compared with those before irradiation,and the n value had no obvious change.The Ag sheath and Bi-2212 superconductor in the superconducting wire before and after irradiation were not hardened by nano-indentation test.In addition,the Cu sheath in YBCO tape has no new precipitates,no shift of diffraction peak and no obvious change of the intensity of all the diffraction peaks after irradiation.The values of I_Cand n value has no difference before and after irradiation.In conclusion,the insignificant changes in microstructure,mechanical properties and superconducting properties after neutron irradiation can be attributed to the fact that no new effective defects were produced by irradiation,which affect the microstructure and properties of superconducting materials.