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Crystals characterized by “metavalent” bonds have specific properties

Crystals characterized by “metavalent” bonds have specific properties

Jean-Yves Raty, researcher FNRS of the Group of Solids Physics, Interfaces and Nanostructures (UR CESAM , SPIN Lab ) of ULiège, has just published two scientific articles noticed in the international journal Advanced Materials. These studies were conducted with the team of Professor Wuttig from Aachen University and collaborators in Belgium, France and Italy. The researchers present an original (ab initio) theoretical study of the chemical bond in solids, a study that allows us to locate all types of crystals on a two-dimensional “map”.

” The peculiarity of this map is that, if it clearly separates semiconducting, metallic, ionic and resonant crystals (such as graphite), an important part of the map is occupied by crystals in which the bonds are” incomplete “. explains Jean-Yves Raty . These connections, however, that ensure the cohesion of the crystal, are in fact too many to the number of available electrons, which is why we called them “métavalentes” or MVB for Metavalent Bonding. “

This two-dimensional map is even more interesting when one considers certain electronic, optical or vibrational properties. Indeed, it appears that the metavalent bonds are responsible for rather unique behaviors and that the compounds presenting these connections are most often good materials for heat recovery and its transformation into electricity (thermoelectricity), topological insulators, superconductors, or materials usable for phase change data recording in new types of fast and non-volatile memories.

On a two-dimensional map where the axes represent the amount of electrons transferred between atoms and those actually shared by neighbors, the different types of crystals occupy distinct regions (semiconductors, metallic, ionic). An area represented in green contains crystals whose bonds are incomplete, described as ‘metavalent’. When we look at the atoms, we see that these bonds are formed by the delocalization (in green) of initially covalent (red) bonds, to form bonds ‘softer’ (the ‘hardness’ of the bonds is here represented in a symbolic way by springs), but also much more polarizable.

” Our calculations have already been partly confirmed by experiments conducted by Professor Wuttig; the latter will also present our results at the ULiège on Thursday, February 7th “

” Of course, our work needs to be pursued to better explain these metavalent links and to know how far they can be manipulated to create innovative materials with exacerbated features. The question has just been asked by a leading editorialist and noted in the journal Science, “concludes Jean-Yves Raty.

source: Université de Liège – Belgium

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