Annealing effects on the Pb-doped 2223 phase under various temperatures and oxygen pressures

doi:10.1016/0921-4534(89)90150-0

Physica C: Superconductivity

Volume 159, Issue 6, 1 August 1989, Pages 789-793

https://doi.org/10.1016/0921-4534(89)90150-0 Get rights and content

Abstract

Annealing effects on the Pb doped 2223 type superconductor Pb_0.35Bi_1.73Sr_1.89Ca_1.86Cu_3.0O_y at various temperatures (200– 800°C) and oxygen pressures (P_O2=0.2–500 atm and in vacuum) are reported. XRD, SEM and TEM examinations indicated that the annealing below 800°C under oxidizing atmosphere generally brought about a segregation of a Ca₂PbO₄-like phase and (Sr,Ca)₂CuO₃ on the surface of the original particles. The particles of the 2223 phase kept their shape and remained well-crystallized but changed to a lead-poor or lead-free composition as seen from a change in the structural modulation wave length from 47 Å to 27 Å. These results have strongly suggested that these two modulation modes correspond to different chemical compositions, one rich in Pb as Pb/Bi≅ $15$ and the other Pb free, Pb/Bi≅0. Under P_O2⪖100 atm at 300°C the oxygen content in the remaining 2223 phase seemed to have increased as suggested from a contraction of the c-axis. When the annealing temperature was raised to 600°C at P_O2=100 atm, a complete decomposition to a perovskite phase, (Sr,Ca) (Pb,Bi)O₃, CuO and Ca₂PbO₄ occurred surprisingly. Under reduced oxygen pressures, the precipitation did not occur.

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We studied the isothermal annealing behavior of the Pb-doped BPSCCO 2223 superconductor in ambient oxygen at temperatures ranging from 650°C to 800°C by resistivity measurement and TGA analysis. It is found that upon annealing under oxidizing conditions a Ca₂PbO₄-like phase is formed, the sample weight and resistivity increase, suggesting incorporation of oxygen. A two dimensional diffusion model of Pb²⁺ in Bi₂-O₂ planes is proposed, and the activation energy for Pb²⁺ diffusion is determined to be 1.47eV.
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Segregation and dissolution reactions of the 2223 phase in the Bi, Pb-Sr-Ca-Cu-O system on annealing in air
1994, Physica C: Superconductivity and its applications
Thermal behavior of the Pb-substituted Bi-2223 phase was examined by characterizing samples annealed at 500°C to 850°C in air and also those subsequently reheated at 850°C in air by XRD, SEM and magnetic measurements. Very interesting reactions occurred, which were segregation of precipitates on annealing below 830°C and dissolution of the precipitates on subsequent reheating at 850°C into the 2223 phase. The precipitates were identified as Sr_2.5Bi_0.5Pb₃Ca₂CuO₂. The precipitation and the dissolution were clearly confirmed by morphological observations of a fixed portion of a sample before and after heat treatments. These results strongly suggest that the 2223 phase changes its composition reversibly between the relatively Pb-rich composition stabilized above 850°C and relatively Pb-poor ones stabilized in essentially the same structure below 830°C. However, T_c remained almost constant at 113 K.
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Annealing effects on the Pb-doped 2223 phase under various temperatures and oxygen pressures

Abstract

Jpn. J. Appl. Phys.

Jpn. J. Appl. Phys.

Jpn. J. Appl. Phys.

Jpn. J. Appl. Phys.