Co系超伝導酸化物の結晶構造と短範囲規則積層

抄録

Neutron powder diffraction patterns of 2H- and 3R-Na_xCoO₂·yD₂O (x~0.35, y~1.3), which show superconductivity with Tc of about 4.7 K, show conspicuous diffuse maxima presumed to originate from the Na/D₂O part in addition to sharp reflections due to the CoO₂ part. The structure is treated as an interpenetration of two layered structures, the CoO₂ part (a₁=b₁=2.82 Å) and the Na/D₂O part (a₂=b₂=3.26 Å). A model of the short-range-order stacking of the Na/D₂O part is expressed and diffuse scattering intensities simulated using the matrix method satisfactorily explain the neutron diffraction patterns. Information about atomic coordinates was obtained based on superstructure expression with A=B=2a₁=a₂√3=5.64 Å including short-range order stacking.