Revised superconducting phase diagram of hole-doped Na(x)(H3O)(z)CoO2 x yH(2)O |
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Authors: | Milne C J Argyriou D N Chemseddine A Aliouane N Veira J Landsgesell S Alber D |
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Institution: | Hahn-Meitner-Institut, Glienicker Strasse 100, Berlin D-14109, Germany. |
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Abstract: | We have studied the superconducting phase diagram of NaxCoO2.yH(2)O as a function of electronic doping, characterizing our samples both in terms of Na content x and the Co valence state. Our findings are consistent with a recent report that intercalation of H3O+ ions into NaxCoO2, together with water, acts as an additional dopant, indicating that Na substoichiometry alone does not control the electronic doping of these materials. We find a superconducting phase diagram where optimal T(C) is achieved through a Co valence range of 3.24-3.35, while T(C) decreases for materials with a higher Co valence. The critical role of dimensionality in achieving superconductivity is highlighted by similarly doped nonsuperconducting anhydrous samples, differing from the superconducting hydrate only in interlayer spacing. |
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