Mechanism of host-layer restacking in HgxTiS2

High-resolution transmission electron microscopy has been used to observe t he host-layer restacking process in situ during HgxTiS2 (1.24 greater than or equal to x greater than or equal to 0.00) deintercalation to better unde rstand the role of elastic strain in reaction dynamics and phase formation for this low-valent system (Hgdelta+, delta much less than 1). Hg forms nov el incommensurate one-dimensional guest chains that occupy channels between the host layers. These channels undergo trigonal prismatic (TP)-to-distort ed trigonal antiprismatic (DTAP) coordination restacking during deintercala tion. Initially, a small metastable TP-coordinated, empty-gallery region fo rms. This region usually undergoes rapid restacking to octahedral coordinat ion (1T-TiS2), which induces an intragallery TP-to-DTAP HgxTiS2 phase trans ition to minimize elastic host-layer strain. Occasionally, TP empty-gallery regions become too large to allow coherent gallery restacking, resulting i n host-layer fault/crack formation. TP and DTAP intercalate lamella can rea dily form coherent lamellar intergrowths, resulting in lamellar mixed-phase regions forming during deintercalation. (C) 11998 Academic Press.