Dynamics of water in the Na0.3 CoO2 1.4 H2 O superconductor

Quasielastic neutron scattering is employed to characterize the diffusion of water molecules that are present between the CoO2 layers in the 4.3 K oxyhydrate superconductor Na0.3 CoO2 1.4 H2 O. Dynamic measurements were performed at temperatures between 3.5 K and 315 K. Significant quasielastic scattering was only observed for temperatures of 235 K and higher where only highly constrained diffusive motion is present, similar to what is seen for water confined in pores. Approximately 80% and 100% (depending on the temperature) of the water molecules remain immobile (i.e., frozen) on the time scale of the measurements (10-9 s). For the mobile water molecules, a model in which the molecules perform localized jumps between Na sites can be used to describe the data. The dynamics of the mobile water molecules does not show a significant change at the superconducting transition temperature.