title: Revised superconducting phase diagram of hole-doped Na(x)(H3O)(z)CoO2 x yH(2)O.
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.
authors.affiliation: Hahn-Meitner-Institut, Glienicker Strasse 100, Berlin D-14109, Germany.
authors.forename: C J
authors.initials: CJ
authors.lastname: Milne
authors.forename: D N
authors.initials: DN
authors.lastname: Argyriou
authors.forename: A
authors.initials: A
authors.lastname: Chemseddine
authors.forename: N
authors.initials: N
authors.lastname: Aliouane
authors.forename: J
authors.initials: J
authors.lastname: Veira
authors.forename: S
authors.initials: S
authors.lastname: Landsgesell
authors.forename: D
authors.initials: D
authors.lastname: Alber