OXYGEN INTERCALATION AND INTERGRANULAR COUPLING IN THE 110-K BI1.7PB0.3SR1.8CA2CU2.8O9.45+DELTA SUPERCONDUCTOR

The effect of the carrier-density variation on the crystal structure a nd properties of Bi1.7Pb0.3Sr1.8Ca2Cu2.8O9.45+delta was studied by con trolling the oxygen content. The kinetics of oxygen sorption are found to depend on the temperature and the partial pressure of oxygen durin g annealing. Also the oxygen trade is exactly reversible. The hole con centration p in the [CuO]+p sheets changes from 0.188 to 0.312 holes/C uO by heat treatment of the superconducting samples at appropriate oxy gen partial pressures. The c parameter also decreases by 0.2% with var iation of the hole concentration in this range. The high-T(c) phase is also found to be stable against the reannealing process. However, two additional peaks are observed in the x-ray-diffraction patterns of al l samples which depend only on the oxygen content. The change in the c ritical temperature due to the hole concentration is similar to other p-type high-T(c) cuprates. The intragranular transition and the Joseph son phase locking temperature determined from ac-susceptibility measur ements correspond to the midpoint temperature of resistivity transitio n and zero-resistivity temperature, respectively. Although the intragr anular transition temperature changes in a range of 2.5 K, the intergr anular coupling is much more sensitive to the chemical modification in CuO sheets and it varies in a range of 40 K. With oxygen intercalatio n, the Josephson phase locking temperature of intergrain junctions app roaches that of the intragrain value and the maximum value of T(c). Th is result suggests that the anionic vacancies at grain boundaries play a special role in the Josephson coupling.