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Novel phase diagram of superconductor NaxCoO2-yH2O in a 75 % relative humidity

Hiroto Ohta·Chishiro Michioka·Yutaka Itoh·Kazuyoshi Yoshimura
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Abstract

We succeeded in synthesizing the powder samples of bilayer-hydrate sodium cobalt oxide superconductors NaxCoO2-yH2O with Tc = 0 ~ 4.6 K by systematically changing the keeping duration in a 75 % relative humidity atmosphere after intercalation of water molecules. From the magnetic measurements, we found that the one-day duration sample does not show any superconductivity down to 1.8 K, and that the samples kept for 2 ~ 7 days show superconductivity, in which Tc increases up to 4.6 K with increasing the duration. Tc and the superconducting volume fraction are almost invariant between 7 days and 1month duration. The 59Co NQR spectra indicate a systematic change in the local charge distribution on the CoO2 plane with change in duration.

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Hiroto Ohta, Chishiro Michioka, Yutaka Itoh, Kazuyoshi Yoshimura. 2005-08-08. Novel phase diagram of superconductor NaxCoO2-yH2O in a 75 % relative humidity. https://doi.org/10.1143/jpsj.74.3147

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