First-principles study of the optical properties of MgxTi1-xH2

Michiel J. van Setten, S. Er, G. Brocks, Robert A. de Groot, Gilles A. de Wijs

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Abstract

Thin films of MgxTi1-x show an optical black state upon hydrogenation. We calculate the dielectric function and the optical properties of MgxTi1-xH2, x=0.5, 0.75, and 0.875 using first-principles density-functional theory. We argue that the black state is an intrinsic property of these compounds, unlike similar optical phenomena observed in other metal hydride films. The structures of MgxTi1-xH2 are represented either by simple ordered or quasirandom structures. The density of states has a broad peak at the Fermi level, composed of Ti d states; hence, both interband and intraband transitions contribute to the optical response. Ordered structures have a plasma frequency of ~3 eV. The plasma frequency drops below 1 eV in disordered structures, which - as a result of interband transitions - then show a low reflection and considerable absorption in the energy range of 1-6 eV, i.e., a black state.
Original languageUndefined
Pages (from-to)125117/1-125117/8
Number of pages8
JournalPhysical review B: Condensed matter and materials physics
Volume79
Issue number12
DOIs
Publication statusPublished - 2009

Keywords

  • METIS-257189
  • IR-61346

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