X-ray and electron diffraction study of intercalates AgxTaS2

A single crystal X-ray diffraction study of Ag0.23TaS2 (a = 0.3324 nm, c = 3.948 nm, space group R3m) of a twinned crystal (the observe and the reverse form of the rhombohedron both present) confirms the second stage structure known from powder data. Tantalum atoms are in trigonalprismatic coordination by sulfur atoms (TaS = 0.2475 nm) whereas silver atoms, being located in trigonally distorted tetrahedra of sulfur (AgS = 0.230 nm (1 ×), AgS = 0.265 nm (3 ×)), occupy a fraction of the sites of a honeycomb lattice between sandwiches of TaS2. At 100 K silver atoms are ordered two-dimensionally on a hexagonal 2a × 2a superlattice. Crystals of the stage-2 phase show considerable lattice disorder due to stacking faults. Electron microscopy and diffraction of stage-2 crystals Ag0.39TaS2 grown by vapour transport show that microdomains with hexagonal 2a × 2a ordering are formed below room temperature from a hexagonal a √3 × a √3 superlattice. Complex ordering patterns are observed on cooling. Crystals of composition Ag0.5TaS2 obtained by vapour transport, being intergrowths of stage-1 and stage-2, also show complicated ordering phenomena of the intercalated silver.