Electronic Principles of Some Trends in Properties of Metallic Hydrides

Abstract

Due to their extensive present, important and versatile potential applications, metal hydrides (MH) are among the most investigated solid-state systems. Theoretical, numerical and experimental studies have provided a considerable knowledge about their structure and properties, but in spite of that, the basic electronic principles of various interactions present in MH have not yet been completely resolved. Even in the simplest MH, i.e. alkali hydrides (Alk-H), some trends in physical properties, . Int. J. Mod. Phys. B 2010.24:703-710. Downloaded from www.worldscientific.com by ROYAL INSTITUTE OF TECHNOLOGY on 02/02/15. For personal use only. 704 N. Ivanović et al.and especially their deviations, are not well understood. Similar doubts exist for the alkaline-earth hydride (AlkE-H) series, and are even more pronounced for complex systems, like transition metaldoped AlkE-H, alanates and borohydrides. This work is an attempt of explaining some trends in the physical properties of Alk-H and AlkE-H, employing the Bader analysis of the charge distribution topology evaluated by first-principle all-electron calculations. These results are related to some variables commonly used in the explanation of experimental and calculated results, and are also accompanied by simple tight-binding estimations. Such an approach provides a valuable insight in the characteristics of M-H and H-H interactions in these hydrides, and their possible changes along with external parameters, like temperature, pressure, defect or impurity introduction. The knowledge of these basic interactions and processes taking place in simple MH are essential for the design and optimisation of complex MH-systems interesting for practical hydrogen storage applications.

Hydride–Hydride Bonding Interactions in the Hydrogen Storage Materials AlH3, MgH2, and NaAlH4

“…A very recent computational study of some metal hydrides reported a saddle point in ρ ( r ) between two hydrogen atoms in 4 , although this was not analyzed further 11. Moreover, a recent experimental study of 4 assigned a significant amount of charge (0.25 e Å −3 ) to the region between the bridging hydrogen atoms,12 in pleasing agreement with our computational results.…”

“…We turn now to consideration of two other light binary metal hydrides, LiH ( 5 ) and NaH ( 6 ), the calculated electron densities of which have been reported before,11 although the values cited were incomplete. These two alkali metal systems adopt the rock salt structure, with hydride ions occupying all octahedral holes in an fcc array of metal ions, but the smaller cation in 5 allows a close H⋅⋅⋅H approach of 2.85 Å (cf.…”

Electronic Principles of Hydrogen Incorporation and Dynamics in Metal Hydrides

“…They are also systems of considerable theoretical interest [15][16][17][18][19][20][21][22][23][24][25] convenient for investigation of fundamental interactions that are expected to be important in new complex materials [26][27][28][29][30][31][32]. Although significant experimental and theoretical work has been devoted to the study of metal hydrides, some of their fundamental features, such as details of valence and conduction bands and energy gap structures, the charge transfer and the charge distribution, the origin and the importance of various contributions to the bonding between metal and hydrogen (M-H) and hydrogen and hydrogen (H-H), are not yet fully clarified.…”

“…A complete elaboration of these topics from the first principles is indispensable for understanding of H-behavior in metallic systems in general. Moreover, extensive data about metal hydrides have been obtained and explained using various, and sometimes contradictory, concepts [15][16][17][18][20][21][22][23][24][25][26][33][34][35][36][37][38][39]. However, a coherent approach valid for all metal hydrides is still missing.…”

“…For that purpose we extended our previous experimental [33,44,45], and known numerical [20,23,32,44,65] results by first-principle calculations of the electronic structures of various metal hydrides using the Full Potential Augmented Plane Waves extended (FP-APW+lo) and the Full Potential Linearized Augmented Plane Waves (FP-LAPW+LO) with addition of local orbitals methods, as implemented in the WIEN2k software package [73], and the pseudopotentials method, as implemented in Abinit software package.…”