Synchrotron X-ray Group, National Institute for Materials Science^* Hahn-Meithner-Institut, Germany^** Korea Atomic Energy Research Institute, Korea^***
○Mitsuko Onoda^* Kazunori Takada^* Dimitri Argyriou^** Yong Nam Choi^*** Takayoshi Sasaki^*

Hydrated sodium cobaltate Na(x)CoO2 yH2O has been reported to be a superconductor with a T(c) of about 5 K. Neutron diffraction patterns of deuterated sodium cobaltate show conspicuous diffuse maxima presumed to originate from deuterated sodium part in addition to sharp reflections due to CoO2 part. The structure is treated as an interpenetration of two layered subsystem structures, CoO2 part (a=0.28nm) and deuterated sodium part (a=0.33). A model of short-range order stacking of deuterated sodium parts is expressed using four possible configurations. The sequences, in which neighboring sheets have the same configuration, do not occur, and the other sequences occur with the same probability. Diffuse scattering intensities simulated using the matrix method satisfactorily explain the broad maxima observed in neutron diffraction patterns.