Abstract
The superconducting properties of sintered high-Tc superconductor bulk deteriorate gradually with time when the calcined powder for fabrication is exposed to the atmosphere. We examined the conditions of moisture and carbon in degraded samples by means of thermal desorption spectroscopy (TDS). In TDS spectra of the calcined powder of Bi-2223, a peak at m⁄z=44(CO2+) appeared in the temperature range between 773 and 873 K when the powder adsorbed moisture and carbon dioxide. When the calcined powder was kept in a carbon dioxide atmosphere, the peak at m⁄z=44(CO2+) was not observed, which was the same as in the TDS spectra measured after calcination. This means that the deterioration in quality of the calcined powder was caused by the adsorption of moisture and carbon dioxide. Microscopic Raman images and EPMA maps showed that carbon was segregated in the grain boundary of the polycrystalline Bi-2223 sintered bulk.
