A novel treasure map for functional materials
Tailoring the properties of materials is one of the major goals of material science. Three physicists of RWTH Aachen University, together with colleagues from Liège, Milan and Prague, describe in their publication „Revisiting the Nature of Chemical Bonding in Chalcogenides to Explain and Design their Properties“ a novel approach to design functional materials.Carl-Friedrich Schön, Jakob Lötfering and Professor Matthias Wuttig from the I. Institute of Physics (IA), RWTH Aachen University were able to develop a treasure map that separates different types of chemical bonding, i.e. covalent, metallic and ionic bonding, as taught in high school chemistry classes. Remarkably, the compounds investigated in their publication show a novel type of chemical bonding, which they coin „metavalent bonding “. These metavalent bonds are responsible for the unique property portfolio of chalcogenides, compounds featuring oxygen, sulfur, selenium or tellurium. Chalcogenides are widely employed to convert sunlight or excess heat into electricity in photovoltaics or thermoelectric elements, respectively. The treasure map now provides the option to explain and predict the property trends required for these applications. It presents a huge leap towards the tailoring of material properties and the discovery of novel high-performance functional materials. The work of the Aachen physicists was published in the “Hall of Fame” section of the esteemed journal “Advanced Materials”.
Figure 1: Quantum-chemical treasure map: A material’s position is determined by the coordinates “Electrons Transferred (ET)” and “Electrons Shared (ES)”. ET describes the relative number of electrons transferred between bonding partners upon bond formation, while ES is the number of shared electrons. Different colors classify different materials according to their properties. Choosing ES and ET as map coordinates separates the various flavors of chemical bonding into distinct areas. Ionic compounds (black) typically exhibit high ET values and low ES values and are hence located in the bottom right corner. Covalently bonded materials (red) feature relative low ET values and high ES values. They are positioned at the top left of the map. Electron delocalization is characteristic for metallic bonding (blue). ES and ET are both low in this case and metals are located in the left bottom part of the map. The competition between electron localization and delocalization is the cornerstone of the novel metavalent bond (green), which can thus be observed in the center of the map.