Oxygen intercalation and intergranular coupling in the 110-K Bi1.7Pb0.3Sr1.8Ca2Cu2.8O9.45+δ superconductor

Abstract

The effect of the carrier-density variation on the crystal structure and properties of Bi1.7Pb0.3Sr1.8Ca2Cu2.8O9.45+δ was studied by controlling the oxygen content. The kinetics of oxygen sorption are found to depend on the temperature and the partial pressure of oxygen during annealing. Also the oxygen trade is exactly reversible. The hole concentration p in the [CuO]+p sheets changes from 0.188 to 0.312 holes/CuO by heat treatment of the superconducting samples at appropriate oxygen partial pressures. The c parameter also decreases by 0.2% with variation of the hole concentration in this range. The high-Tc phase is also found to be stable against the reannealing process. However, two additional peaks are observed in the x-ray-diffraction patterns of all samples which depend only on the oxygen content. The change in the critical temperature due to the hole concentration is similar to other p-type high-Tc cuprates. The intragranular transition and the Josephson phase locking temperature determined from ac-susceptibility measurements correspond to the midpoint temperature of resistivity transition and zero-resistivity temperature, respectively. Although the intragranular transition temperature changes in a range of 2.5 K, the intergranular coupling is much more sensitive to the chemical modification in CuO sheets and it varies in a range of 40 K. With oxygen intercalation, the Josephson phase locking temperature of intergrain junctions approaches that of the intragrain value and the maximum value of Tc. This result suggests that the anionic vacancies at grain boundaries play a special role in the Josephson coupling.

Source-reported materials — not catalogue approval

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