Structural, optical, and electrical properties ofMgyTi1−yHxthin films

Abstract

Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The structural, optical, and electrical transformations induced by hydrogen absorption and/or desorption in Mg-Ti thin films prepared by co-sputtering of Mg and Ti are investigated. Highly reflective in the metallic state, the films become highly absorbing upon H absorption. The reflector-to-absorber transition is fast, robust, and reversible over many cycles. Such a highly absorbing state hints at the coexistence of a metallic and a semiconducting phase. It is, however, not simply a composite material consisting of independent MgH 2 and TiH 2 grains. By continuously monitoring the structure during H uptake, we obtain data that are compatible with a coherent structure. The average structure resembles rutile MgH 2 at high Mg content and is fluorite otherwise. Of crucial importance in preserving the reversibility and the coherence of the system upon hydrogen cycling is the accidental equality of the molar volume of Mg and TiH 2 . The present results point toward a rich and unexpected chemistry of Mg-Ti-H compounds.

Absorption of Hydrogen by Thin Films

“…В двухкомпонентных плёнках на основе магния Mg y Ti 1y и Mg y Ni 1y процессы поглощения водорода также взаимосвязаны с изменениями их оптических свойств и электропроводимости [41][42][43]. Это во многом связано с тем, что фаза MgH 2 является ди-электриком и имеет менее компактную решётку, чем магний.…”

“…Коэффициент пропускания световых волн у такого материала с ростом содержания в нём водорода увели-чивается, а коэффициент отражения уменьшается (рис. 5, а) [41]. Происходящие при этом структурные изменения коррелируют с ростом электросопротивления (рис.…”

First-principles study of the optical properties ofMgxTi1−xH2

“…The equality of the molar volumes of TiH 2 and Mg has been used to explain the structural stability of these metastable thin film alloys. 15,16 Notten and co-workers [20][21][22] and Borsa et al 6,15 showed that for a high titanium content, x Շ 0.8, the structure of the hydrides is fluoritelike. Hydrides with a lower titanium content adopt a rutilelike structure, similar to that of ␣-MgH 2 .…”

“…In experiments, usually somewhat less than two hydrogen atoms per metal atom are absorbed. 15 Electrochemically 1.7 hydrogen atoms per metal atom can be absorbed and desorbed reversibly. 25 The high-pressure crystalline phase Mg 7 TiH 16 contains two hydrogen atoms per metal atom.…”

“…The structure of these Mg-Ti compounds and the origin of the black state are a topic of intensive research. [15][16][17] Obtaining structural data for these systems is difficult. Single crystals cannot be grown under standard conditions, as bulk Mg-Ti alloys, as well as their hydrides, are thermodynamically unstable.…”