Structure topology in silver(I)-(poly)chalcogenide halides: a helpful tool to understand structure relations and properties

Recent progress in the field of silver(I)-chalcogenide halides and silver(1)-polychalcogenide halides led to the discovery of a reasonable number of new phases, solid solutions and even a new substance class of materials with favorable electronic and thermoelectric properties. Most of these new compounds are characterized by a pronounced ion mobility, polymorphism, and complex structures, which result in severe problems during the structure solution, the refinement, and even the description of the crystal structures. Herein we report on a very simple but effective building principle and a topological structure approach, which are both based on the separate description of anion substructures and the introduction of discrete building blocks. Such a topological principle helps to understand the complex structural relations and allows one to discuss all known chalcogenide and polychalcogenide halides in a continuous sequence of compounds. Following this principle it is possible to understand physical properties and to predict new phases in the system.