Structure, Oxygen Stoichiometry and Superconductivity of La-Sr-Ba-Cu-O

• Main Authors: Yuan Chung-Chien, 袁中堅
• Other Authors: Huey-Churn I. Kao
• Format: Others
• Language: zh-TW
• Published: 1994
• Online Access: http://ndltd.ncl.edu.tw/handle/19698507680646081521

碩士 === 淡江大學 === 化學學系 === 82 === In this paper, a series of single phase La-Sr-Ba-Cu-O compound with tetragonal triple-perovskite structure is prepared by solid state reaction method. These sample are calcined at 1000.degree.C for 6hr, gound and pressed, sintered at 850-950 .degree.C in flowing O2 atmosphere for 8hr and then followed with furnace cooling. The resulting material are examined by powder X-ray diffraction and thermal analysis to know the phase purity. The solubility limits are 0.ltoreq.x.ltoreq.0.900. La- Sr-Ba-Cu-O are superconductor besides x=0,0.050, which are semiconductors. In general, their Tc are in between 28-48K and increased with increasing x. From thermal analysis, we find that peritectic point of them are between 1080-1105.degree.C, weight loss is about(0.35.plmin.0.05)O2/mole, and enthalpy is about (42.plmin.4)kJ/mole. With the increased of Sr substitution, unit cell parameters in a-axes is decreased monotonically, c-axes is decreased for x=0-0.500, and then tend to increase slowly, volume is also decreased at first, and keeps constant after x=0.700. As x is increased, oxygen stoichiometry is decreased but hole concentration is increased. In order to have a Tc(zero) higher then 40K, unit cell a-axes, oxygen stoichiometry and hole concentration of La-Sr-Ba-Cu-O must be in between 3.8769-3.8885A ,14.017-14.120 and 0.290-0.325. There is a highest Tc when x=0.700, its unit cell a-axes, oxygen stoichiometry and hole concentration is 3.8803A, 14.071, 0.307, respectively.