THE EFFECT OF ISOELECTRONIC CATION SUBSTITUTION AND DEOXYGENATION OF BI8SR8-XCA4+XCU9O33+E-DELTA SUPERCONDUCTORS ON THE THERMOPOWER AND RESISTIVITY

The resistivity-rho(T) and thermopower S(T) of the 2212-structure-type Bi8Sr8-xCa4+xCu9O33+E-delta series of solid solutions with x = 0, 1, 2, 3 and 4 have been examined. The compounds sintered in air show an excess of oxygen content whose maximum E=1.25 is found for x=0 with a tendency to decrease with increasing x. Deoxygenation of x=2 solution (vacuum at elevated temperatures) by delta> 1.4 leads to structural degradation. The as-sintered solutions are superconducting below T(c)almost-equal-to 69-74 K. The latter can be optimized with respect to oxygen content. For x=2 and delta-almost-equal-to0.1 the T(c) increases to 94 K. Both S(T) and rho(T) vary monotonically with delta from metallic to nonmetallic-type behavior. The solutions become nonmetallic and nonsuperconducting at delta-greater-than-or-equal-to 0.46 (x=2). The substitution parameter (x) affects the resistivity and thermopower in the same way as delta but by one order of magnitude weaker in comparison with changes of the oxygen-content: -(DELTA-S/DELTA-E)T=250 kappa=11+/-3-mu-VK-1 per ox. at. (oxygen atom) per fu. (formula unit), (DELTA-S/DELTA-delta)T=250-kappa=96+/-15-mu-VK-1 per ox. at. per fu..