X-ray and transmission electron microscopy investigations of the new solids In5S5Cl, In5Se5Cl, In5S5Br, and In5Se5Br

摘要

The compounds In(5)Ch(5)X (Ch = S, Se; X = Cl, Br) represent new mixed valence solids with indium occurring simultaneously in three different oxidation states: In+, In3+ and In2+ where the latter appears as covalently bonded dumbbells (In-2)(4+). Although the ionic formulation (In(5)Ch(5)X = In+ 2In(3+) (In-2)(4+) 5Ch(2-) X-) is the same for all compounds, they crystallise in two structure types (In(5)Ch(5)Cl-type: monoclinic, P2(1)/m, Z = 2; In(5)Ch(5)Br-type: orthorhombic, Pmn2(1), Z = 2). Ignoring the distribution of the halogen atoms, the anionic partial structure is very similar in both structure types. The main difference is an exchange of (In+) by (In-2)(4+) and vice versa on selected positions. This is possible due to the nearly identical coordination of both ions (tri-capped trigonal prisms). HRTEM investigations show remarkable differences in the real structures of In(5)Ch(5)Cl and In(5)Ch(5)Br. In contrast to the perfectly ordered crystals of the bromides, the chlorides exhibit a variety of nanoscaled crystal defects, i.e. twinning, polylamellar inter-growth of polymorphs and lamellar intergrowth of structurally related compounds as demonstrated in In5S5Cl/In6S7. The occurrence of these defects is discussed using an appropriate structure model.