Common features of (Pb,Sr) and (Pb,Ca) 1212 superconductors produced on O<sub>2</sub> at normal pressure
M Hechtl; J Bernhard; K F Renk; M Hechtl; Inst. fur Angewandte Phys., Regensburg Univ., Germany; J Bernhard; Inst. fur Angewandte Phys., Regensburg Univ., Germany; K F Renk; Inst. fur Angewandte Phys., Regensburg Univ., Germany
Журнал:
Superconductor Science and Technology
Дата:
1994-06-01
Аннотация:
We prepared superconducting samples of the 1212 systems (Pb<sub>0.5</sub>Sr<sub>0.5</sub>)Sr<sub>2</sub>(Y<sub>1-x</sub>Ca<sub>x</sub>)Cu<sub>2</sub>O<sub>7+or- delta </sub> and (Pb<sub>0.5</sub>Ca<sub>0.5</sub>)Sr<sub>2</sub>(Y<sub>1-x</sub>Ca<sub>x</sub>)Cu<sub>2</sub>O<sub>7+or- delta </sub> in an oxidizing atmosphere of normal O<sub>2</sub> pressure. By variation of the Y/Ca ratio an optimum of the temperature at which superconductivity sets in, T<sub>c</sub><sup>ons</sup>, was found for x=0.80 in both systems. X-ray diffraction studies give evidence that the range of stability of the 1212 structure with respect to x is slightly greater in the (Pb,Ca) system than in the (Pb,Sr) system. We observed an increase of the lattice constants with x, suggesting that structural stress increases with Ca content. The loss of weakly bound O after post-annealing and quenching the samples in liquid N<sub>2</sub> improves the normal state conductivity and increases T<sub>c</sub><sup>ons</sup> and also T<sub>c</sub><sup>R=0</sup> for most of the samples.
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