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arXiv · 0910.1003

First principles modelling of magnesium titanium hydrides

Süleyman Er·Michiel J. van Setten·Gilles A. de Wijs·Geert Brocks
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Abstract

Mixing Mg with Ti leads to a hydride Mg(x)Ti(1-x)H2 with markedly improved (de)hydrogenation properties for x < 0.8, as compared to MgH2. Optically, thin films of Mg(x)Ti(1-x)H2 have a black appearance, which is remarkable for a hydride material. In this paper we study the structure and stability of Mg(x)Ti(1-x)H2, x= 0-1 by first-principles calculations at the level of density functional theory. We give evidence for a fluorite to rutile phase transition at a critical composition x(c)= 0.8-0.9, which correlates with the experimentally observed sharp decrease in (de)hydrogenation rates at this composition. The densities of states of Mg(x)Ti(1-x)H2 have a peak at the Fermi level, composed of Ti d states. Disorder in the positions of the Ti atoms easily destroys the metallic plasma, however, which suppresses the optical reflection. Interband transitions result in a featureless optical absorption over a large energy range, causing the black appearance of Mg(x)Ti(1-x)H2.

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Süleyman Er, Michiel J. van Setten, Gilles A. de Wijs, Geert Brocks. 2009-10-06. First principles modelling of magnesium titanium hydrides. https://doi.org/10.1088/0953-8984%2F22%2F7%2F074208

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