Complex high-temperature phase transitions in Li2B12H12 and Na2B12H12

Verdal, Nina; Her, Jae‐Hyuk; Stavila, Vitalie; Soloninin, Alexei V.; Babanova, Olga A.; Skripov, A. V.; Udovic, Terrence J.; Rush, J. J.

doi:10.1016/j.jssc.2014.01.006

Cited by 119 publications

(189 citation statements)

References 33 publications

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“…This behaviour is in line with several previously described high temperature metal-closoborane polymorphs, i.e. β-M 2 B 12 H 12 (M = Li, Na, Ag) 30,36 and β-M 2 B 10 H 10 (M = Na, Ag). 16,36 The Na-atoms in β-Na 2 B 12 Cl 12 are located in 4b and 24d Wyckoff sites with partial occupancies (0.53(6) and 0.24(1), respectively).…”

Section: Structural Characterizationsupporting

confidence: 92%

Halogenated Sodium-closo-Dodecaboranes as Solid-State Ion Conductors

et al. 2017

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Sodium compounds containing large weakly coordinating anions are explored as ion conductors. The halogenated sodium-closo-dodecaboranes (Na 2 B 12 Cl 12 , Na 2 B 12 Br 12 , and Na 2 B 12 I 12 ) are all isostructural (Pa-3) at room temperature. These compounds undergo an order-disorder polymorphic transition to Fm-3m where Na + partially occupies two crystallographic sites and [B 12 X 12 ] 2-anions undergo reorientational motion. These dynamic structural properties promote extreme Na + ion conductivity up to 0.162 S/cm at elevated temperature (500 °C). The polymorphic transition temperatures increase down the halogen group (Cl < Br < I). These temperatures are much higher (475, 525 and 570 °C) than for Na 2 B 12 H 12 (266 °C), which could be related to increasing anion size, mass and the anisotropic electron density in the covalently bound halogens (B-X). The halogens may form Na−X interactions with increasing strength and directionality, which restrict dynamic motion until high temperature. The halogenated sodium-closo-dodecaboranes demonstrate excellent thermal stabilities (up to 500 °C) and may facilitate the development of new high temperature ion conductors.

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Section: Structural Characterizationsupporting

confidence: 92%

Halogenated Sodium-closo-Dodecaboranes as Solid-State Ion Conductors

et al. 2017

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“…The weight loss starts at approximately 580˝C and the dehydrogenation amount reaches 1.9 mass%, which is approximately 29% of the theoretical hydrogen capacity in Na 2 B 12 H 12 . The value is comparable to the reported one (~1.5 mass% at 697˝C) [31].…”

Section: Decomposition Of Anhydrous LIsupporting

confidence: 89%

“…The weight loss starts at approximately 580 °C and the dehydrogenation amount reaches 1.9 mass%, which is approximately 29% of the theoretical hydrogen capacity in Na2B12H12. The value is comparable to the reported one (~1.5 mass% at 697 °C) [31]. The changes of anhydrous Na2B12H12 heated to respective temperatures and subsequently cooled down to room temperature examined by XRD, Raman and 11 B NMR are shown in Figures 5 and 6, respectively.…”

Section: Decomposition Of Anhydrous LIsupporting

confidence: 86%

Thermal Decomposition of Anhydrous Alkali Metal Dodecaborates M2B12H12 (M = Li, Na, K)

Akiba

2015

Energies

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Metal dodecaborates M 2/n B 12 H 12 are regarded as the dehydrogenation intermediates of metal borohydrides M(BH 4 ) n that are expected to be high density hydrogen storage materials. In this work, thermal decomposition processes of anhydrous alkali metal dodecaborates M 2 B 12 H 12 (M = Li, Na, K) synthesized by sintering of MBH 4 (M = Li, Na, K) and B 10 H 14 have been systematically investigated in order to understand its role in the dehydrogenation of M(BH 4 ) n . Thermal decomposition of M 2 B 12 H 12 indicates multistep pathways accompanying the formation of H-deficient monomers M 2 B 12 H 12´x containing the icosahedral B 12 skeletons and is followed by the formation of (M 2 B 12 H z ) n polymers. The decomposition behaviors are different with the in situ formed M 2 B 12 H 12 during the dehydrogenation of metal borohydrides.

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“…Both precursors show a characteristic endothermic peak at the temperature of their respective structural phase transition, as previously described. 24,25 No such event is observed for the 1 : 1 mixture indicating that Na 2 (B 12 H 12 ) 0.5 (B 10 H 10 ) 0.5 does not undergo a phase transition within this temperature window. Besides the first heating cycle, we also show DSC data of the third heating cycle, which almost coincides with the first cycle, and demonstrates the stability of the equimolar Fig.…”

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confidence: 96%