The role of the water molecules in novel superconductor, Na0.35CoO2 · 1.3H2O

In order to investigate the role of the water molecules in Na0.35CoO2 · 1.3H2O, we synthesized superconducting Na0.35CoO2 · 1.3H2O and nonsuperconducting Na0.35CoO2 · 0.7H2O, and measured their normal-state magnetic susceptibilities. The susceptibility of Na0.35CoO2 · 1.3H2O has an enhancement below ∼150 K probably caused by ferromagnetic fluctuation, whereas no such enhancement was observed in Na0.35CoO2 · 0.7H2O. The water molecules in Na0.35CoO2 · 1.3H2O may work to shield random coulomb potential of the Na ions with smoother potential at the CoO2 layer. This effect may account for the appearance of superconductivity in Na0.35CoO2 · 1.3H2O. [Copyright &y& Elsevier]