Superconductivity, charge ordering and structural properties of alpha   and beta-NaxCoO2.y(H2O, D2O)
  Two series of &#61537;alpha and beta-NaxCoO2 materials have been prepared by means of Na deintercalation from the parent &#61537;alpha-NaCoO2 and &#61538;beta-Na0.6CoO2 phases, respectively. The &#61537;alpha-NaxCoO2 materials undergo a clear phase transition from the hexagonal to the beta-phase like monoclinic structure along with Na deintercalation. Measurements of resistivity and magnetization demonstrated the presence notable charge ordering transitions in both alpha and beta-NaxCoO2 with 0.4 < x < 0.5 below 100K. Bulk Superconductivity has been observed in the hydrated &#61537;alpha-NaxCoO2.1.3H2O at ~4.5K and in &#61538;beta-NaxCoO2.1.3H2O at \~4.3K. Intercalation of D2O in alpha and beta-Na0.33CoO2 also yields superconductivity at slightly lower temperatures. It is worthy to note that, despite of the structural difference, the alpha-, beta- and gamma-NaxCoO2 .yH2O materials show up notable commonalities in their essential physical properties, e.g. superconductivity and charge ordering transitions. 
Y. G. Shi, H. X. Yang, H. Huang, X. Liu, and J.Q. Li