Electronic Structure of Intercalation Compounds of CoxNbS2

Abstract

Cobalt intercalation into niobium disulfide with layered structure is presented. Powder X-ray diffraction study reveals that single-phase CoxNbS2 forms in the compositional range of 0.15 ≤ x ≤ 0.55. The hexagonal lattice parameters a and c monotonically increase with cobalt content up to x ∼ 0.5, while a and c are constant and decreasing from x = 0.5 to 0.55, respectively. The temperature dependence of electric resistivity shows metallic behavior at 0.15 ≤ x < 0.49 whereas semiconducting behavior is seen at 0.49 ≤ x ≤ 0.55, so that metal−semiconductor transition occurs at the composition x = 0.49. The temperature dependence of magnetic susceptibility obeys a Curie−Weiss law in the whole compositional range, suggesting localized electronic behavior around Co ions. The valance state of Co in CoxNbS2 was evaluated as divalent from effective Bohr magneton. The ab initio computation based on density functional theory was performed for NbS2 and Co1/3NbS2. The dz2 band arising from the NbS6 trigonal-prism crysta...