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Enhanced supercurrent density in polycrystalline YBa2Cu3O7-δ at 77 K from calcium doping of grain boundaries


With the discovery of high-temperature superconductivity1, it seemed that the vision of superconducting power cables operating at the boiling point of liquid nitrogen (77 K) was close to realization. But it was soon found that the critical current density Jc of the supercurrents that can pass through these polycrystalline materials without destroying superconductivity is remarkably small1,2. In many materials, Jc is suppressed at grain boundaries2,3,4, by phenomena such as interface charging and bending of the electronic band structure5,6,7,8,9. Partial replacement (‘doping’) of the yttrium in YBa2Cu3O7-δ with calcium has been used to increase grain-boundary Jc values substantially, but only at temperatures much lower than 77 K (ref. 9). Here we show that preferentially overdoping the grain boundaries, relative to the grains themselves, yields values of Jc at 77 K that far exceed previously published values. Our results indicate that grain-boundary doping is a viable approach for producing a practical, cost-effective superconducting power cable operating at liquid-nitrogen temperatures.

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Figure 1: Illustration of the doping superlattices and bilayers investigated.
Figure 2
Figure 3: Temperature dependence of the critical current densities Jc of grain boundaries with various doping configurations, indicating the strong enhancement of Jc in doping heterostructures.
Figure 4: Dependence of the grain boundary critical current density Jc on the thickness of the doped top layer in doping bilayers.


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We are grateful for valuable discussions with D. G. Schlom. This work was supported by the Bundesministerium für Bildung und Forschung. H.H. thanks the Royal Dutch Academy of Sciences for its support.

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Hammerl, G., Schmehl, A., Schulz, R. et al. Enhanced supercurrent density in polycrystalline YBa2Cu3O7-δ at 77 K from calcium doping of grain boundaries . Nature 407, 162–164 (2000).

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