Study on the change of MgB2 after long-time storage

• Main Author: 徐碩志
• Other Authors: 張秋男
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/gn5z3p

碩士 === 國立臺灣師範大學 === 物理學系 === 96 === We report our work on the study of the change of MgB2 thin film after long-time storage(the ageing film). The film was prepared by Sung-IK et al. of Pohang University of Science and Technology, Korea about two years ago. The hysteresis of the film in the magnetic field range of -50000 Oe to +50000 Oe was obtained by a superconducting quantum interference device (SQUID). The critical current density Jc was deduced by using Bean model and it was found to be 6.4×10^6 A/cm2 at 5 K. The critical current density Jc becomes about an order of magnitude smaller than the value published by Sung-IK Lee et al. in PRL87,087002(2001). The X-ray diffraction measurements showed that the ageing film contains MgO. The lattice constant deduced from it indicates that the lattice constant c is a little shorter than that of the fresh film. The combined data of the X-ray diffraction and the X-ray near-edge absorption spectra suggests that the ageing film of MgB2 oxidized gradually in two years and some MgO and B2O3 had been produced. The impurities of MgO and B2O3 in the ageing film do not increase the current density. It is possible that these impurities are mainly on the surface of the sample. This is consistent with the observations in the X-ray near-edge absorption spectra deduced from the sample current of B K edge, which shows mainly the signals of B2O3.