RELATIONSHIPS AMONG SEEBECK COEFFICIENT, OXYGEN-CONTENT AND SUPERCONDUCTIVITY OF BI-SR-CA-CUPRATES

The correlations among Seebeck coefficient, oxygen content and superco nducting property were examined for four Bi-Sr-Ca-Cu-O systems, i.e., a 2223-phase oxide, Bi1.84Pb0.34Sr1.91Ca2.03Cu(3.06)O(10.1-z,) and thr ee 2212-isostructural oxides, Bi2Sr2-xCa1+xCu2Oy (x = 0, 0.5 and 1.0), Temperature-Programmed-Desorption (TPD) as well as Temperature-Progra mmed-Oxidation (TPO) measurements revealed that small amounts of oxyge n (2-3 x 10(-5) mol/g) were sorbed and desorbed reversibly for all oxi des examined in the temperature ranges of ca. 100-400 degrees C and ca . 250-600 degrees C, respectively, In goad agreement with such sorptio n-desorption behavior, the Seebeck coefficient (Q) of each oxide was f ound to change reversibly with changing temperature in the range of 10 0-600 degrees C, This means that Q is a reversible function of oxygen content for each oxide, For the 2212-oxides, Q values at 100 degrees C were in the range of ca. -10 - + 10 mu V/K and increased to the posit ive direction almost linearly with decreasing oxygen content, though t he increments were somewhat different depending on composition, This i ndicates that oxygen content is directly related with the carrier conc entration of each sample, Interestingly, T-c of each 2212-oxide was ob served to go through a maximum with oxygen content. It was found that the highest T-c was reached at the oxygen content at which Q was broug ht to around zero at 100 degrees C for each oxide, These results sugge st that there exists an optimum carrier concentration giving the highe st T-c in common for the three 2212-oxides tested.