Structural and electronic transport properties of NaxCoO2

Structure and transport properties of the layered materials NaxCoO2 (0.48 ≤ x ≤ 0.76) have been investigated. With the increase of x, the in-plane lattice parameter a increases while the lattice parameter c decreases. The lattice parameter c of our samples is much smaller than that of the samples whose Na content was controlled by chemical de-intercalation from Na0.77CoO2 [Foo et al., Phys. Rev. Lett. 92 (2004) 247001]. The temperature dependence of electrical resistivity of NaxCoO2 shows that all the samples remain metallic and the resistivity reaches a minimum around x = 0.68. A jump in dρ/dT was observed at certain temperature, which depends on x. The difference of electrical transport property between NaxCoO2 prepared by solid-state reaction and NaxCoO2 obtained by chemical de-intercalation from Na0.77CoO2 was also discussed by considering the lattice parameter difference.