Ordering in Intercalated Ni Atoms and Electron Density Distributions of Layered Compounds NixTiS2

A structural study of layered compounds Ni x TiS 2 ( x = 0.30, 0.37, and 0.63) by X-ray and electron diffraction analyses was performed to investigate both the ordered atomic arrangement and disordering behavior of intercalated Ni atoms, and the nature of the chemical bond from the electron density distribution obtained by the maximum entropy method. The 2 a ×2 a ×2 c and \(\sqrt{3}a{\times}\sqrt{3}a{\times}2c\) superstructures of the Ni atoms are observed for x = 0.30 and 0.37 at room temperature, and they disappear at 420 and 425 K with second-order-like behavior. A partial 2 a ×2 a ×2 c ordered arrangement of the Ni atoms is observed at room temperature and disappears at approximately 650 K for x = 0.63. The electron density distribution reveals that the bonding between Ni and S atoms in the van der Waals gap layer has a covalent nature. Such characteristic behavior decreases the interlayer lattice spacing after intercalating Ni atoms into TiS 2 .