INFLUENCE OF MOISTURE AND CARBON ADSORBED IN CALCINED POWDERS ON THE SUPERCONDUCTING PROPERTIES OF BI-2223 SINTERED BULKS

The superconducting properties of sintered high-T-c superconductor bul k deteriorate gradually with time when the calcined powder for fabrica tion is exposed to the atmosphere. We examined the conditions of moist ure and carbon in degraded samples by means of thermal desorption spec troscopy (TDS). In TDS spectra of the calcined powder of Bi-2223, a pe ak at m/z=44(CO2+) appeared in the temperature range between 773 and 8 73 K when the powder adsorbed moisture and carbon dioxide. When the ca lcined 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 m easured after calcination. This means that the deterioration in qualit y of the calcined powder was caused by the adsorption of moisture and carbon dioxide. Microscopic Raman images and EPMA maps showed that car bon was segregated in the grain boundary of the polycrystalline Bi-222 3 sintered bulk.