Crystal structure and elementary properties ofNaxCoO2(x=0.32

The crystal structures of ${\mathrm{Na}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ phases based on three-layer $\mathrm{Na}\mathrm{Co}{\mathrm{O}}_{2}$, with $x=0.32$, 0.51, 0.60, 0.75, and 0.92, determined by powder neutron diffraction, are reported. The structures have triangular $\mathrm{Co}{\mathrm{O}}_{2}$ layers interleaved by sodium ions, and evolve with variation in Na content in a more complex way than has been observed in the two-layer ${\mathrm{Na}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ system. The phases with highest and lowest Na content studied ($x=0.92$ and 0.32) are trigonal, with three $\mathrm{Co}{\mathrm{O}}_{2}$ layers per cell and octahedral Na ion coordination. The intermediate compositions have monoclinic structures. The $x=0.75$ compound has one $\mathrm{Co}{\mathrm{O}}_{2}$ layer per cell, with Na in octahedral coordination and an incommensurate superlattice. The $x=0.6$ and 0.51 phases are also single layer, but the Na is found in trigonal prismatic coordination. The magnetic behavior of the phases is similar to that observed in the two-layer system. Both the susceptibility and the electronic contribution to the specific heat are largest for $x=0.6$.