The crystal growth and characterization of NaxCoO2 and NaxCoO2yH2O
  A systematic study of NaxCoO2 (x=0.50 - 0.90) and NaxCoO2 yH(D)2O (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. 
D.P. Chen, H.C. Chen, A. Maljuk, A. Kulakov, H. Zhang, P. Lemmens and   C.T. Lin