Static and dynamical disorder ofNiCl2clusters intercalated in graphite

We report an experimental study on static and dynamical disorder of nickel dichloride intercalated in graphite, by means of extended x-ray-absorption fine-structure measurements on the Ni K edge at different temperatures. As we have shown in a previous paper, at room temperature the ${\mathrm{NiCl}}_2$ molecules are intercalated between the hexagonal planes of graphite in the form of clusters or islands without significant short-range distortion. However, the question remained unsolved if the graphite lattice can induce a structural distortion of the Cl positions such that the disorder is increased but the Ni-Cl average distance is unchanged. Our present results, performed at low temperature, confirm our previous data of the interatomic distances but indicate that the ${\mathrm{NiCl}}_2$ molecule undergoes a static deformation upon intercalation. The dynamical properties of the nickel dichloride clusters measured by the behavior of Debye-Waller factors versus temperature show the same trend as the crystal in the first shell but indicate the presence of a softening of the second-shell bond due to the clustering.