Abstract
THE two superconducting phases YBa2Cu4O8 (124), containing double Cu–O chains, and Y2Ba4Cu7O15 (247), containing both single and double Cu–O chains, were originally discovered as lattice defects in the 90-K superconductor YBa2Cu3O7 (123)1. The synthesis of bulk superconducting 124 may be effected by a high-oxygen-pressure annealing technique2,3 and by reaction with ambient oxygen in the presence of alkali carbonates4. The oxygen stoichiometry of 124 is much more stable against high temperatures than that of 123 (ref. 2), a feature that is important for practical applications. But the lower Tc (80 K) of 124 presents a major obstacle to practical uses of this phase at liquid-nitrogen temperature (77 K). Here we report that partially substituting Ca for Y in 124 increases Tc. A superconducting transition of ∼90 K was achieved for the composition Y0.9 Ca0.1, Ba2Cu4O8.
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Miyatake, T., Gotoh, S., Koshizuka, N. et al. Tc increased to 90 K in YBa2Cu408 by Ca doping. Nature 341, 41–42 (1989). https://doi.org/10.1038/341041a0
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DOI: https://doi.org/10.1038/341041a0
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