Chemical Bonding in Intermetallic Compounds

Yuri Grin
Max Planck Institute for Chemical Physics of Solids, Dresden, Allemagne.
Jeudi 21 Avril 2016, 11h00
bibliothèque LCT, tour 12 - 13, 4^ème étage

     Intermetallic compounds reveal chemical and physical behaviors interesting for applications and may serve as basic components for materials design. In particular chemical catalysis, thermoelectric or heavy-fermion behaviors are in focus recently. An attempt to find a direct link between the properties and the crystal structure as well the atomic interactions for this group of inorganic substances revels often a lack of reliable information on all three, crystal structure, bonding and properties, hindering studies on their relationship.
     In particular chemical bonding in intermetallic compounds is a rather open question. An application of modern quantum-chemical tools like Electron Localizability approach (ELI-D) opens access to the bond definition in real space [1], allows revealing of the - on first glance unexpected - relation between organometallic and intermetallic compounds of rare-earth metals [2] or opening the way to unique definition of the important categories of chemical bond descriptors like covalence or ionicity [3] or polarity [4]. This gives a possibility of Zintl-like interpretation for large group of intermetallic phases [4,5] and yields a connection to the basic information about possible band structure [6].
     The ELI-D approach allows differentiation of covalent, ionic and lone-pair contributions to the atomic interactions [4]. So, the formation of the lone pairs around the defects in the Ge framework in the clathrate Ba₈Ge₄₃□₃ and the covalent Ba-Au interactions in the clathrate Ba₈Au_xGe_46-x-y□_y as well polar interactions Cu-Se and Cu-Sn in Cu₂SnSe₃ [7] were detected. Both findings yield to the special features of the electronic DOS, which were confirmed by measurements of electronic and thermal transport. Bonding-caused features in the boride TmAlB₄ result in new magnetic interactions [8]. Understanding of the chemical bonding in intermetallic compounds opens a way to novel redox-based preparation routes. So the binary clathrates Ba₈Si₄₆ [9] and Na₂₄Si₁₃₆ [10] - were prepared and their transport properties were investigated. Another bonding-based concept dealing with the intermetallic phases is the isolated-site model for catalysis. New catalysts for semi hydrogenation of acetylene based on the well-crystallized intermetallic compounds GaPd and Al₄Fe₁₃ were suggested employing the ideas of the covalent atomic interactions in intermetallic compounds [11,12].

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