Single-crystal growth and investigation of NaxCoO2 and NaxCoO2•yH2O -: art. no. 024506

A systematic study of NaxCoO2 (x=0.50-0.90) and NaxCoO2.yH(D)(2)O (x=0.26-0.42, y=1.3) has been performed to determine phase stability and the effect of hydration on the structural and superconducting properties of this system. We show that a careful control of the Na deintercalation process and hydration dynamics is possible in single crystals of this system. Furthermore, we give experimental evidence that the dependence of the superconducting transition temperature on Na content is much weaker than reported earlier. Implications of this effect for the understanding of the superconducting phase diagram are discussed.