The correlations among Seebeck coefficient, oxygen content and superconducting property were examined for four Bi-Sr-Ca-Cu-O systems, i.e., a 2223-phase oxide, Big
1.84Pb
0.34Sr
1.91Ca
2.03Cu
3.06O
10.1-z, and three 2212-isostructural oxides, Bi
2Sr
2-xCa
1+xCu
2O
y (
x=0, 0.5 and 1.0). Temperature-Programmed-Desorption (TPD) as well as Temperature-Programmed-Oxidation (TPO) measurements revealed that small amounts of oxygen (2-3×10
-5mol/g) were sorbed and desorbed reversibly for all oxides examined in the temperature ranges of ca. 100-400°C and ca. 250-600°C, respectively. In good agreement with such sorption-desorption behavior, the Seebeck coefficient (
Q) of each oxide was found to change reversibly with changing temperature in the range of 100-600°C. This means that
Q is a reversible function of oxygen content for each oxide. For the 2212-oxides,
Q values at 100°C were in the range of ca. -10-+10μV/K and increased to the positive direction almost linearly with decreasing oxygen content, though the increments were somewhat different depending on composition. This indicates that oxygen content is directly related with the carrier concentration of each sample. Interestingly,
Tc of each 2212-oxide was observed to go through a maximum with oxygen content. It was found that the highest
Tc was reached at the oxygen content at which
Q was brought to around zero at 100°C for each oxide. These results suggest that there exists an optimum carrier concentration giving the highest
Tc in common for the three 2212-oxides tested.
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