Observation of bulk superconductivity in NaxCoO2•yH2O and NaxCoO2•yD2O powder and single crystals -: art. no. 217001

Poly- and single-crystalline NaxCoO2 has been successfully intercalated with H2O and D2O as confirmed by x-ray diffraction and thermogravimetric analysis. Resistivity, magnetic susceptibility, and specific heat measurements show bulk superconductivity with T-c close to 5 K in both cases. The substitution of deuterium for hydrogen has an effect on T-c of less than 0.2 K. Investigation of the resistivity anisotropy of NaxCoO2.yH(2)O single crystals shows (a) almost zero resistivity below T-c, and (b) an abrupt upturn at T(*)similar to52 K in both the ab plane and the c direction. The implications of our results on the possible superconducting mechanism will be discussed.