| Title |
Low Temperature orthorhombic - to - tetragonal Phase transition by Fe - doping in YBa ( Cu , Fe ) O System |
| Authors |
김찬중(Chan Joong Kim); 김택남(Taik Nam Kim); 김기백(Ki Baik Kim); 권양철(Sang Chul Kwon); 이희균(Hee Gyoun Lee); 원동연(Dong Yeon Won) |
| Abstract |
The low temperature phase transition of high-Tc superconducting phase has been investigated in Fe-doped YBaCuO systems by X-ray diffraction analysis, optical microscopy, transmission electron microscopy and electrical resistivity measurement. The phase transition from orthorhombic to tetragonal in YBa₂(Cu_(1-x) Fe_x)₃O_(7-y) superconductor is induced by replacing Cu with Fe. A mixture of the orthorhombic and tetragonal phases exists in specimens containing Fe of about x=0.03. In orthorhombic platelike grains are observed striations which are related to the formation of twins in the grains. The phase transition can be easily identified by the disappearance of the striations in platelike grains under polarized light. As Fe content increases, the twin spacing in orthorhombic phase becomes narrow. In the tetragonal phase at x$gt;0.03, the fine tweed structure is observed instead of the twin structure of the orthorhombic phase. The c parameter does not change even though the phase change occurs, implying that the tetragonal phase in Fe-doped specimen contains more oxygen than that in undoped specimen. The zero resistance temperature(Tc) and oxygen content decrease with Fe content. Nevertheless, the specimen containing Fe up to 2 at% shows high Tc of 84K, suggesting that the super conductivity in YBa₂(Cu_(1-x), Fe_x)₃O_(7-y) is more related to the oxygen content than the crystal structure. |