Dynamic high-resolution transmission electron microscopy has been used to provide the first detailed dynamic atomic-level observations of lamellar deintercalation reaction processes. Mercury-intercalated titanium disulfide was chosen as the model weak-charge-transfer intercalation system for comprehensive investigation. Complete deintercalation of stage-1 material was induced in-situ by resistive and electron-beam heating. Deintercalation onset was most often observed at the external-most guest layers, consistent with greater external host-layer flexibility. Onset also frequently occurred at internal guest layers, which is associated with the presence of surface and internal lattice defects. Deintercalation generally progresses away from the onset layer(s) to form primarily randomly-staged regions, with occasional stage ordering. Guest and host-layer behavior during deintercalation provides strong support for the applicability of the Daumas-Hrold guest-island model of staging. These observations include guest-island formation/deintercalation and formation of stable staggered domain walls.

A combination of high resolution transmission electron microscopy (HRTEM) and X-ray powder diffraction was used to solve and refine the complex structure of this intercalation system.

This model system forms unusual four-dimensional compounds consisting of interpenetrating three-dimensional partially incommensurate monoclinic host (mercury) and guest (titanium disulfide) sublattices. These sublattices share commensurate a and c axes, but are incommensurate along the b axis. The material can exist in two structural modifications (with monoclinic angles, , of either 102 or 96) which are very similar, differing only by a minor shift of host layers. Mercury layers are comprised of infinite one-dimensional chains embedded in sulfur channels of rectangular cross section created by host-layer restacking.

Deintercalation induces a transition from the = 102 to = 96 modification via a host-layer stacking shift along the mercury chain (b) axis, changing the coordination of the sulfur channels from trigonal prismatic to trigonal antiprismatic. The mercury chains exhibit substantial axial thermal disorder, which is enhanced during deintercalation. The material exhibits significant metallic guest-guest intrachain bonding and novel guest-host interactions between the mercury chains and sulfur channels, as evidenced by the intralayer off-chain-axis modulation of the mercury positions ( 0.2 ).


Last updated: March 06, 2017

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