Normal state properties of NaxCoO2 yH2O

Crystal structure, magnetic susceptibility, electrical and thermal transport, and heat capacity data are reported for single crystals (from floating zone growths) and polycrystalline samples of NaxCoO2 yH2O (0.35 < x < 0.75, 0 < y < 1.4). The evolution of the various normal state properties with variable sodium and water content will be presented and discussed. Particular emphasis will be placed on separating the intrinsic properties of these materials from effects due to impurity phases and disorder. For example, we find that polycrystalline samples of NaxCoO2 processed using temperatures between 750 and 850DGC are only single phase for x = 0.74 #+ 0.02. Samples prepared with lower values of x contain measurable amounts of Co3O4 and other impurity phases. The measured electronic properties of these materials will be compared to those expected from electronic structure calculations (D. Singh and others). Evidence for strong electronic correlations based on the normal state properties of the sodium cobaltates also will be discussed.