A new ternary magnesium–titanium hydride Mg7TiH  with hydrogen desorption properties better than both binary magnesium and titanium hydrides

Kyoi, Daisuke; Sato, Toyoto; Rönnebro, Ewa; Kitamura, Naoyuki; Ueda, Atsushi; Ito, Mikio; Katsuyama, Shigeru; Hara, Shigeta; Noréus, Dag; Sakai, Tetsuo

doi:10.1016/j.jallcom.2003.08.098

Cited by 138 publications

(110 citation statements)

References 17 publications

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“…8,9 We observe a similar crystalline Mg-Ti alloy phase ͑hexago-nal structure͒ when co-sputtering Mg and Ti. In hydrogenated films the formation of a MgH 2 -like rutile phase is observed for low Ti contents ͑y = 0.90͒, whereas in Mg y Ti 1−y with y = 0.80 and y = 0.70, a fluorite-like Mg-Ti-H phase is formed, similar to that identified by Kyoi et al 10 in bulk samples. There are no indications that phase segregation takes place as is the case for Mg-rare-earth systems such as Mg-Gd, Mg-La, and Mg-Y.…”

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confidence: 82%

Mg–Ti–H thin films for smart solar collectors

Borsa

Baldi

Pasturel

et al. 2006

Applied Physics Letters

108

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Mg-Ti-H thin films are found to have very attractive optical properties: they absorb 87% of the solar radiation in the hydrogenated state and only 32% in the metallic state. Furthermore, in the absorbing state Mg-Ti-H has a low emissivity; at 400 K only 10% of blackbody radiation is emitted. The transition between both optical states is fast, robust, and reversible. The sum of these properties highlights the applicability of such materials as switchable smart coatings in solar collectors. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2212287͔ Many metal hydrides behave as switchable mirrors ͑i.e., their optical properties switch from reflective in the metallic state to transparent in the hydrogenated state͒. [1][2][3][4] In addition, magnesium-rare-earth ͑Mg-RE͒ and magnesium-transitionmetal ͑Mg-TM͒ switchable mirrors also exhibit an intermediate highly absorbing optical state on hydrogenation. The possibility to switch a film from a reflective state to an absorbing state suggests that such materials might be interesting for smart solar collectors, which absorb light in normal operation condition and switch to a reflective state to avoid overheating. Limiting the stagnation temperature of the solar collector makes it possible to use cheap materials such as plastics ͑generally not designed for high temperatures͒.In this letter we show that Mg y Ti 1−y thin films prepared by dc magnetron co-sputtering of Mg and Ti at room temperature ͑on quartz and CaF 2 ͒ satisfy the following requirements for a smart solar coating: ͑i͒ high absorption in the solar regime ͑0.5Ͻប Ͻ 4 eV͒, ͑ii͒ low emissivity in the thermal regime ͑ប Ͻ 0.5 eV͒, and ͑iii͒ reversibility. Three compositions are studied in detail: y = 0.70, y = 0.80, and y = 0.90. Typical deposition rates are 2 Å / s for Mg ͑150 W rf power͒, 0.1-1 Å / s for Ti ͑25-160 W dc power͒, and 1.3 Å / s for Pd ͑50 W dc power͒. All the films are covered with a Pd layer ͑10-50 nm͒ to promote dissociation of H 2 and to prevent oxidation of the underlying film.Reflection ͑R͒ and transmission ͑T͒ spectra are measured simultaneously during hydrogenation ͑pressures up to 1 bar H 2 ͒ in a Perkin Elmer Lambda 900 diffraction grating spectrometer ͑0.495Ͻប Ͻ 6.51 eV͒ and a Bruker IFS 66 Fourier transform infrared spectrometer ͑0.2Ͻប Ͻ 1.1 eV͒. The R-T spectra are measured through the transparent substrate at near normal incidence of the incoming beam. Figures 1͑a͒ and 1͑b͒ show the reflection and transmission spectra measured for 200 nm Mg y Ti 1−y / 10 nm Pd films ͑y = 0.90, 0.80, and 0.70͒ in the as-prepared and hydrogenated states ͑in 1 bar H 2 at room temperature͒. In the metallic state ͓Fig. 1͑a͔͒ all the films have a relatively high and featureless reflection that decreases with increasing Ti content.After hydrogen absorption, the reflection is low for all compositions, whereas significant transmission is observed only for the y = 0.90 sample. The combination of low reflection and low transmission in the hydrogenated state ͑y = 0.80 and 0.70 samples͒ gives rise to a highly a...

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supporting

confidence: 82%

Mg–Ti–H thin films for smart solar collectors

Borsa

Baldi

Pasturel

et al. 2006

Applied Physics Letters

108

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“…The stabilization of β-polymorph derived nanoparticles receives special attention in this respect. 42 The hydrogen desorption temperature for this compound is about 130 K lower than that of bulk phase of MgH 2 . It is interesting to note that the crystal structure of Mg 7 TiH x is a super structure of the high pressure β-modification.…”

Section: Studies On Nanoparticlesmentioning

confidence: 85%

Influence of Crystal Structure of Bulk Phase on the Stability of Nanoscale Phases: Investigation on MgH₂ Derived Nanostructures

Vajeeston¹,

Ravindran

Fichtner

et al. 2012

J. Phys. Chem. C

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Phase stability of α-, β-, γ-, and δ′-MgH 2 -derived nanostructures have been investigated using ab initio projected augmented plane wave method. Structural optimizations based on total energy calculations predicted that β-derived nanoparticles and α-derived nanowhiskers are more stable than those derived from other polymorphs. Present study indicates that the crystal structure of the bulk phase plays a significant role on the stabilization of different forms (nanoparticles or nanowhiskers) of nanophases. The predicted critical sizes of the stable β-nanoparticle and α-nanowhisker for MgH 2 are 2.4 and 1.5 nm, respectively. The calculated hydrogen site energies suggest that it is relatively easier to remove hydrogen from the surface of the nanoparticles and nanowhiskers compared to that from bulk crystals. Among the considered nano-objects, removing hydrogen from the β-derived nanocluster is much easier, and hence, the present study suggests that one can use these nanoparticles for practical applications. NMR-related parameters are calculated for different sizes of the nanoclusters and nanowhiskers.

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“…elemental substitutions [22][23][24][25][26] , mechanical alloying 22,25,27 and high-pressure synthesis 28 , have been applied separately or jointly resulting in a formation of a number of improved and promising compounds but none of them reveal outstanding kinetic or/and thermodynamic properties. Novel Mg-TM hydrides (TM = transition metal) have been previously obtained from MgH 2 and different TM or TM hydrides in an anvil cell under mechanical pressure of several GPa 29 30,36 . The same behavior has been reported for disorder FCC Ti-containing Mgbased hydrides [23][24] .…”

Section: Introductionmentioning

confidence: 99%