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, 4ème 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 Ba8AuxGe46-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].
[1] F. R. Wagner et al. Chem. Eur. J. 108, 5724 (2007).
[2] M. V. Butovski et al. Nature Chem. 2, 741 (2010).
[3] D. Bende et al. Chem. Eur. J. 20, 9702 (2014).
[4] D. Bende et al. Inorg. Chem. 54, 3970 (2015).
[5] D. Bende, Yu. Grin, F. R. Wagner, In: Heusler Alloys, Springer, 133ff (2016).
[6] Yu. Grin. In: Comprehensive Inorganic Chemistry II, vol 2. Oxford: Elsevierr, 359ff (2013).
[7] J. Fan et al. Inorg. Chem. 52, 11067 (2013).
[8] T. Mori et al. J. Appl. Phys. 107, 09E112 (2010).
[9] J. Liang et al. Inorg. Chem. 50, 4523 (2011).
[10] M. Beekman et al. Phys. Rev. Lett. 104, 018301 (2010).
[11] M. Armbrüster et al. J. Am. Chem. Soc. 132, 14145 (2010).
[12] M. Armbrüster et al. Nature Materials 11, 690 (2012).