Revised superconducting phase diagram of hole doped Naₓ(H₃O)zCoO₂· yH₂O

الأصل · EN

We have studied the superconducting phase diagram of 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 ions into NaₓCoO₂, together with water, act as an additional dopant indicating that Na sub-stochiometry alone does not control the electronic doping of these materials. We find a superconducting phase diagram where optimal is achieved through a Co valence range of 3.24 - 3.35, while decreases for materials with a higher Co valence. The critical role of dimensionality in achieving superconductivity is highlighted by similarly doped non-superconducting anhydrous samples, differing from the superconducting hydrate only in inter-layer spacing. The increase of the interlayer separation between CoO₂ sheets as Co valence is varied into the optimal region is further evidence for this criticality.