High-Pressure Study of Mn(BH4)2 Reveals a Stable Polymorph with High Hydrogen Density

Nikolay A. Tumanov, Elsa Roedern, Zbigniew Łodziana, Dorrit B. Nielsen, Torben R. Jensen, Alexandr V. Talyzin, Radovan Černý, Dmitry Chernyshov, Vladimir Dmitriev, Taras Palasyuk, Yaroslav Filinchuk

Résultats de recherche: Contribution à un journal/une revueArticleRevue par des pairs


High-pressure behavior of α-Mn(BH4)2 was studied up to 29.4 GPa in diamond anvil cells using powder X-ray diffraction combined with DFT calculations and Raman spectroscopy, and two new polymorphs were discovered. The first polymorph, δ-Mn(BH4)2, forms near 1 GPa and is isostructural to the magnesium analogue δ-Mg(BH4)2. This polymorph is stable upon decompression to ambient conditions and can also be obtained by compression of α-Mn(BH4)2 in a large-volume steel press as well as by high-energy ball milling. It shows a high volumetric density of hydrogen of 125 g H2/L at ambient conditions. δ-Mn(BH4)2 was refined in the space group I41/acd with the cell parameters a = 7.85245(6), c = 12.1456(2) Å, and V = 748.91(1) Å3 at ambient conditions; it can also be described in a stable P-4n2 superstructure. Its thermal stability was studied by in situ X-ray powder diffraction and thermal analysis coupled with mass-spectroscopy. δ-Mn(BH4)2 transforms back to α-Mn(BH4)2 upon heating in the temperature range of 67-109 °C in Ar (1 bar) or H2 (100 bar) atmosphere, and a decomposition is initiated at 130 °C with the release of hydrogen and some diborane. Mn(BH4)2 undergoes a second phase transition to δ′-Mn(BH4)2 in the pressure range of 8.6-11.8 GPa. δ′-phase is not isostructural to the second high-pressure phase of Mg(BH4)2, and its structure was determined in the √2a × c supercell compared to the δ-phase and refined in the space group Fddd with a = 9.205(17), b = 9.321(10), c = 12.638(15) Å, and V = 1084(3) Å3 at 11.8 GPa. Equations of state were determined for α- and δ-Mn(BH4)2.

langue originaleAnglais
Pages (de - à)274-283
Nombre de pages10
journalChemistry of Materials
Numéro de publication1
Les DOIs
Etat de la publicationPublié - 12 janv. 2016
Modification externeOui

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