Effect of Neutron Irradiation on Electrical Properties of Bi_2Sr_2CaCu_2 (Bi-2212) Phase Superconductor

摘要

The effect of neutron irradiation on superconducting properties of Bi_2Sr_2CaCu_2 (Bi-2212) phase superconductor was studied. TRIGA MARK II research reactor with neutron flux of 2.00 × 10~(11)/cm~2s was used as the neutron source. Results between non-irradiated and irradiated samples have been analyzed from the aspects of microstructure and electrical properties. In this work, the bulk samples were prepared using the conventional solid-state reaction method. Molar ratio of Bi_2O_3, Sr_2CO_3, CaCO_3 and CuO were mixed according to its ratio into composition of Bi:Sr:Ca:Cu =2:2:1:2. The samples were sintered at 840℃ during the sample preparation process. Some of the fully synthesized samples were irradiated with neutron irradiation. Neutron irradiation has been proved to promote better flux pinning properties by introducing larger defects in various superconductor ceramics. Enhanced flux pinning centers in the superconductor is responsible in enhancing the critical current, I_c and critical current density, J_c of the irradiated samples. The samples were characterized through X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The transition temperature, T_c and the J_c were measured by using a cryogenic four-point probe system. The XRD patterns for the non-irradiated and irradiated samples show well-defined peaks of which could be indexed on the basis of the Bi-2212 phase structure. XRD patterns also indicate that irradiation did not affect the Bi-2212 superconducting phase. However, the enhancement of J_c was observed in the neutron irradiated sample and this indicates the effectiveness of .neutron irradiation in creating defects that acted as effective flux pinning centers for vortices.