High-Resolution Electron Microscopy of Intercalation Compounds

With regard to intercalation compounds, high resolution electron microscopy is able to provide valuable information on the structural organization of these materials and, hence, can help to solve many of the unresolved issues in intercalation chemistry. For example, conventional HRTEM has already provided the most direct support for the Daumas-Hrold model of staging by direct imaging of D-H domain boundaries, coherent stage-n regions, and guest islands.

However, such static observations are inherently limited in the information they can provide on intercalation/deintercalation reaction processes, staging transitions and dynamics. In contrast to these static observations, the potential of recently developed dynamic high resolution transmission electron microscopy (DHRTEM) to explore these processes at the atomic level is tremendous.

DHRTEM provides a unique and powerful tool for investigating staging processes and related phenomena in layered ICs at the atomic level. Indeed, it is the only technique that allows direct atomic-level imaging of both guest and host layers during staging transformations. Very recently, environmental DHRTEM has been employed to observe intercalation reaction processes at the atomic level for the first time. DHRTEM has also been used to make the first atomic-level observations of staging processes associated with model ionic Ag_+0.17TiS2_0.17- [67] and neutral Hg_1.24TiS₂ [67,68] intercalation compounds. In these studies, it has been shown that such dynamic studies can directly resolve reaction processes and their associated cause-and-effect relationships. The results of these initial efforts with DHRTEM to investigate intercalation mechanisms are summarized below.