Structural stability and pressure-induced phase transitions in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi>MgH</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Vajeeston, Ponniah; Ravindran, P.; Hauback, Bjørn C.; Fjellvåg, Helmer; Kjekshus, Arne; Furuseth, Sigrid; Hanfland, Michael

doi:10.1103/physrevb.73.224102

Cited by 160 publications

(108 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…[13] According to the reported sequence of phase transitions in SiO 2 analogs, the SrI 2 type is most likely structure for phase X [Moriwaki et al, 2006;Vajeeston et al, 2006;Lowther et al, 1999]. However, no orthorhombic solutions satisfied the expected axial ratios for the SrI 2 -type: a:b:c ' 1:2:2.…”

Section: Resultsmentioning

confidence: 99%

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

Grocholski

Shim

Prakapenka

2010

Geophysical Research Letters

View full text Add to dashboard Cite

First‐principles calculations on MgSiO3 suggested a breakdown into MgO + SiO2 at pressure above 1000 GPa with an extremely large negative Clapeyron slope, isolating the lowermost mantles of larger super‐Earths (∼10M⊕) from convection. Similar calculations predicted the same type of breakdown in NaMgF3 to NaF + MgF2 at 40 GPa, allowing for experimental examination. We found that NaMgF3 is stable to at least 70 GPa and 2500 K. In our measurements on MgF2 (an SiO2 analog), we found a previously unidentified phase (“phase X”) between the stability fields of pyrite‐type and cotunnite‐type (49–53 GPa and 1500–2500 K). A very small density increase (1%) at the pyrite‐type → phase X transition would extend the stability of NaMgF3 relative to the breakdown products. Furthermore, because phase X appears to have a cation coordination number intermediate between pyrite‐type (6) and cotunnite‐type (9), entropy change (ΔS) would be smaller at the breakdown boundary, making the Clapeyron slope (dP/dT = ΔS/ΔV) much smaller than the prediction. If similar trend occurs in MgSiO3 and SiO2, the breakdown of MgSiO3 may occur at higher pressure and have much smaller negative Clapeyron slope than the prediction, allowing for large‐scale convection in the mantles of super‐Earth exoplanets.

show abstract

Section: Resultsmentioning

confidence: 99%

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

Grocholski

Shim

Prakapenka

2010

Geophysical Research Letters

View full text Add to dashboard Cite

show abstract

“…Under further compression, several other high-pressure phases (with space group Pa3̅ , Pbc21, Pbca; Pnnm, Fm3m ̅ ) were proposed by theory, 6,33 and the ab initio pseudopotential calculations established the sequence of the phase transition as α → γ → β(Pa-3) → δ(Pbc21) → ε(Pnma). 6,31 Recently, a metastable phase of MgH 2 (I41/amd, space group 141), which meets all the mechanical stability criteria for a tetragonal crystal, has been suggested through full-potential linearized augmented plane-wave (FP-LAPW) calculations. 34 Very recently, a new pressure-induced transition from the α-MgH 2 phase to an orthorhombic CaCl 2 (Pnnm) phase is predicted by ab initio phonon calculations.…”

Section: Computational Detailsmentioning

confidence: 99%

“…However, its slow hydriding/dehydriding kinetics and high dissociation temperature (nearly 573 K) prevent its practical applications on auto mobile technologies. In our recent experimental study 6 we have found that application of pressure on α-MgH 2 transforms it into γ-to-β and β-to-δ′ modifications. Numerous studies have been focused on MgH 2 for improving the problematic sorption kinetics, including mechanical ball milling, 7−12 doping, 10,13−16 and chemical alloying.…”

Section: Introductionmentioning

confidence: 99%

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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…One of the routes that have been considered to overcome these limitations is the addition of dopants and additives to MgH 2 . [6][7][8] Recently, Milosevic et al 9 employed the mechanical milling of NaNH 2 to improve the desorption properties of MgH 2 . It was revealed that with 2 wt% of NaNH 2 and short milling time (∼15min) the best desorption efficiency could be achieved.…”

Section: Author(s) All Article Content Except Where Otherwise Notedmentioning

confidence: 99%

“…Shelyapina et al 18 investigated the effect of mixing of Tm in MgH 2 to accelerate the kinetics of hydrogen. Based on total energy calculations, they estimated the heat of formation and relative stabilities of newly synthesized Ca 7 Ge type hydrides Mg 6 MH 16 (M = Ti, V, and Nb) as compared to MgH 2 . All of the hydrides were found to be less stable than pure MgH 2 .…”

Section: Author(s) All Article Content Except Where Otherwise Notedmentioning

confidence: 99%

Improvement in the hydrogen desorption from MgH2 upon transition metals doping: A hybrid density functional calculations

et al. 2013

View full text Add to dashboard Cite

This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs) by means of hybrid density functional theory (PBE0). On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM’s. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies

show abstract

Structural stability and pressure-induced phase transitions inMgH2

Cited by 160 publications

References 34 publications

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

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

Improvement in the hydrogen desorption from MgH2 upon transition metals doping: A hybrid density functional calculations

Contact Info

Product

Resources

About

Structural stability and pressure-induced phase transitions inMgH2

Cited by 160 publications

References 34 publications

Stability of the MgSiO3 analog NaMgF3 and its implication for mantle structure in super‐Earths

Stability of the MgSiO3 analog NaMgF3 and its implication for mantle structure in super‐Earths

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

Improvement in the hydrogen desorption from MgH2 upon transition metals doping: A hybrid density functional calculations

Contact Info

Product

Resources

About

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

Stability of the MgSiO₃ analog NaMgF₃ and its implication for mantle structure in super‐Earths

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