I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[12714, 14015]
Abstract: Metal borohydrides are a fascinating and continuously expanding class of materials, showing promising applications within many different fields of research. This study presents 17 derivatives of the hydrogen-rich ammonium borohydride, NH4BH4, which all exhibit high gravimetric hydrogen densities (>9.2 wt % of H2). A detailed insight into the crystal structures combining X-ray diffraction and density functional theory calculations exposes an intriguing structural variety ranging from three-dimensional (3D) frameworks, 2D-layered, and 1D-chainlike structures to structures built from isolated complex anions, in all cases containing NH4+ countercations. Dihydrogen interactions between complex NH4+ and BH4– ions contribute to the structural diversity and flexibility, while inducing an inherent instability facilitating hydrogen release. The thermal stability of the ammonium metal borohydrides, as a function of a range of structural properties, is analyzed in detail. The Pauling electronegativity of the metal, the structural dimensionality, the dihydrogen bond length, the relative amount of NH4+ to BH4–, and the nearest coordination sphere of NH4+ are among the most important factors. Hydrogen release usually occurs in three steps, involving new intermediate compounds, observed as crystalline, polymeric, and amorphous materials. This research provides new opportunities for the design and tailoring of novel functional materials with interesting properties.
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Aug 2020
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I11-High Resolution Powder Diffraction
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Abstract: Hemiammine lithium borohydride, LiBH4·1/2NH3, is characterized and a new Li+ conductivity mechanism is identified. It exhibits a Li+ conductivity of 7 × 10−4 S cm−1 at 40 °C in the solid state and 3.0 × 10−2 S cm−1 at 55 °C after melting. The molten state of LiBH4·1/2NH3 has a high viscosity and can be mechanically stabilized in nano-composites with inert metal oxides and other hydrides making it a promising battery electrolyte.
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Apr 2020
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I11-High Resolution Powder Diffraction
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Abstract: Light weight and cheap electrolytes with fast multi-valent ion conductivity can pave the way for future high-energy density solid-state batteries, beyond the lithium-ion battery. Here we present the mechanism of Mg-ion conductivity of monoammine magnesium borohydride, Mg(BH4)2·NH3. Density functional theory calculations (DFT) reveal that the neutral molecule (NH3) in Mg(BH4)2·NH3 is exchanged between the lattice and interstitial Mg2+ facilitated by a highly flexible structure, mainly owing to a network of di-hydrogen bonds, N–Hδ+⋯−δH–B and the versatile coordination of the BH4− ligand. DFT shows that di-hydrogen bonds in inorganic matter and hydrogen bonds in bio-materials have similar bond strengths and bond lengths. As a result of the high structural flexibiliy, the Mg-ion conductivity is dramatically improved at moderate temperature, e.g. σ(Mg2+) = 3.3 × 10−4 S cm−1 at T = 80 °C for Mg(BH4)2·NH3, which is approximately 8 orders of magnitude higher than that of Mg(BH4)2. Our results may inspire a new approach for the design and discovery of unprecedented multivalent ion conductors.
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Mar 2020
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I11-High Resolution Powder Diffraction
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Mathias
Jorgensen
,
Patrick T.
Shea
,
Anton W.
Tomich
,
Joel B.
Varley
,
Marnik
Bercx
,
Sergio
Lovera
,
Radovan
Cerny
,
Wei
Zhou
,
Terrence J.
Udovic
,
Vincent
Lavallo
,
Torben
Jensen
,
Brandon C.
Wood
,
Vitalie
Stavila
Abstract: Solid-state ion conductors based on closo-polyborate anions combine high ionic conductivity with a rich array of tunable properties. Cation mobility in these systems is intimately related to the strength of the interaction with the neighboring anionic network and the energy for reorganizing the coordination polyhedra. Here, we explore such factors in solid electrolytes with two anions of the weakest coordinating ability, [HCB11H5Cl6]– and [HCB11H5Br6]–, and a total of eleven polymorphs are identified for their lithium and sodium salts. Our approach combines ab initio molecular dynamics, synchrotron X-ray powder diffraction, differential scanning calorimetry, and AC impedance measurements to investigate their structures, phase-transition behavior, anion orientational mobilities, and ionic conductivities. We find that M(HCB11H5X6) (M = Li, Na, X = Cl, Br) compounds exhibit order-disorder polymorphic transitions between 203 and 305 °C, and display Li and Na superionic conductivity in the disordered state. Through detailed analysis, we illustrate how cation disordering in these compounds originates from a competitive interplay among the lattice symmetry, the anion reorientational mobility, the geometric and electronic asymmetry of the anion, and the polarizability of the halogen atoms. These factors are compared to other closo-polyborate-based ion conductors to suggest guidelines for optimizing the cation-anion interaction for fast ion mobility. This study expands the known solid-state, poly(carba)borate-based materials capable of liquid-like ionic conductivities, unravels the mechanisms responsible for fast ion transport, and provides insights into the development of practical superionic solid electrolytes.
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Jan 2020
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Anna
Wolczyk
,
Biswajit
Paik
,
Toyoto
Sato
,
Carlo
Nervi
,
Matteo
Brighi
,
Seyedhosein Payandeh
Gharibdoust
,
Michele R. R.
Chierotti
,
Motoaki
Matsuo
,
Guanqiao
Li
,
Roberto
Gobetto
,
Torben
Jensen
,
Radovan
Cerny
,
Shin-ichi
Orimo
,
Marcello
Baricco
Abstract: In this paper, the Li5(BH4)3NH complex hydride, obtained by ball milling LiBH4 and Li2NH in various molar ratio, has been investigated. Using X-ray powder diffraction analysis the crystalline phase has been indexed with an orthorhombic unit cell with lattice parameters a = 10.2031(3), b = 11.5005(2) and c = 7.0474(2) Å at 77 °C. The crystal structure of Li5(BH4)3NH has been solved in space group Pnma, and refined coupling DFT and synchrotron radiation X-ray powder diffraction (SR-XPD) data of a 3LiBH4:2Li2NH ball milled sample after annealing. Solid state NMR measurements confirmed the chemical shifts calculated by DFT from the solved structure. The DFT calculations confirmed the ionic character of this Lithium rich compound. Each Li+ cation is coordinated by three BH4- and one NH2- anion in a tetrahedral configuration. The room temperature ionic conductivity of the new orthorhombic compound is close to10-6 S/cm at room temperature, with activation energy of 0.73 eV.
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May 2017
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[12714]
Abstract: Two new bimetallic sodium or potassium lanthanum borohydrides, NaLa(BH4)4 and K3La(BH4)6, are formed using La(BH4)3 free of metal halide by-products. NaLa(BH4)4 crystallizes in an orthorhombic crystal system with unit cell parameters, a = 6.7987(19), b = 17.311(5), c = 7.2653(19) Å and space group symmetry Pbcn. This compound has a new structure type built from brucite-like layers of octahedra (hcp packing of anions) with half of the octahedral sites empty leading to octahedral chains similar to rutile (straight chains) or α-PbO2 (zig-zag chains). K3La(BH4)6 crystallizes in the monoclinic crystal system with unit cell parameters a = 7.938(2), b = 8.352(2), c = 11.571(3) Å, β = 90.19(6)° and space group P21/n with a double-perovskite type structure. Thermogravimetric analysis shows a mass loss of 5.86 and 2.83 wt% for NaLa(BH4)4 and K3La(BH4)6, respectively, in the temperature range of room temperature to 400 °C. Mass spectrometry shows that hydrogen release starts at 212 and 275 °C for NaLa(BH4)4 and K3La(BH4)6, respectively and confirms that no diborane is released. Sieverts’ measurements reveal that 2.03 and 0.49 wt% of hydrogen can be released from the NaLa(BH4)4 and K3La(BH4)6, respectively, during the second hydrogen desorption cycle at the selected physical condition for hydrogen absorption.
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Nov 2016
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I11-High Resolution Powder Diffraction
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Abstract: Rare earth metal borohydrides show a number of interesting properties, e.g., Li ion conductivity and luminescence, and the series of materials is well explored. However, previous attempts to obtain M(BH4)3 (M = La, Ce) by reacting MCl3 and LiBH4 yielded LiM(BH4)3Cl. Here, a synthetic approach is presented, which allows the isolation of M(BH4)3 (M = La, Ce) via formation of intermediate complexes with dimethyl sulfide. The cubic c-Ce(BH4)3 (Fm3̅c) is isostructural to high-temperature polymorphs of A(BH4)3 (A = Y, Sm, Er, Yb) borohydrides. The larger size of the Ce3+ ion makes the empty void in the open ReO3-type framework structure potentially accessible to small guest molecules like H2. Another new rhombohedral polymorph, r-M(BH4)3 (M = La, Ce), is a closed form of the framework, prone to stacking faults. The new compounds M(BH4)3 (M = La, Ce) can be combined with LiCl in an addition reaction to form LiM(BH4)3Cl also known as Li4[M4(BH4)12Cl4]; the latter contains the unique tetranuclear cluster [M4(BH4)12Cl4]4– and shows high Li-ion conductivity. This reaction pathway opens a way to synthesize a series of A4[M4(BH4)12X4] (M = La, Ce) compounds with different anions (X) and metal ions (A) and potentially high ion conductivity.
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Oct 2016
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I11-High Resolution Powder Diffraction
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Abstract: Three new perovskite-type bimetallic alkali metal strontium borohydride compounds, α-MSr(BH4)3 (M = K, Rb, Cs), have been synthesized and investigated by in-situ synchrotron radiation powder X-ray diffraction, thermal analysis combined with mass spectrometry and Sievert’s measurements. The bimetallic borohydrides were synthesized via an addition reaction between Sr(BH4)2 and MBH4 (M = K, Rb, Cs) by mechanochemical treatment. The Sr(BH4)2 – NaBH4 system, which was treated in a similar manner, did not undergo reaction. All three α-MSr(BH4)3 compounds crystallize in the orthorhombic crystal system at room temperature: KSr(BH4)3 (P21cn), a = 7.8967(6), b = 8.2953(7), and c = 11.508(1) Å (V = 753.82(12) Å3). RbSr(BH4)3 (Pbn21), a = 8.0835(3), b = 8.3341(4), and c = 11.6600(5) Å (V = 785.52(6) Å3). CsSr(BH4)3 (P22121), a = 8.2068(9), b = 8.1793(9), and c = 6.0761(4) Å (V = 407.87(7) Å3). All three compounds are perovskite-type 3D framework structures built from distorted [Sr(BH4)6] octahedra. High-temperature polymorphs are identified to form at 258, 220 and 150 °C for MSr(BH4)3, M = K, Rb and Cs, respectively. The new compounds are thermally stable and decompose at T > 360 °C into SrB6, SrH2 and MBH4 (M = K, Rb, Cs).
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Nov 2015
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I11-High Resolution Powder Diffraction
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Nikolay A.
Tumanov
,
Elsa
Roedern
,
Zbigniew
Łodziana
,
Dorrit B.
Nielsen
,
Torben R.
Jensen
,
Alexandr V.
Talyzin
,
Radovan
Cerny
,
Dmitry
Chernyshov
,
Vladimir
Dmitriev
,
Taras
Palasyuk
,
Yaroslav
Filinchuk
Abstract: High-pressure behavior of 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 analog, 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 one of the highest volumetric densities 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, 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 powder X-ray 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 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, V = 1084(3) Å3 at 11.8 GPa. Equations of state were determined for α- and δ-Mn(BH4)2.
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Nov 2015
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[9031]
Abstract: A new series of solvent- and halide-free ammine strontium metal borohydrides Sr(NH3)n(BH4)2 (n=1, 2, and 4) and further investigations of Ca(NH3)n(BH4)2 (n=1, 2, 4, and 6) are presented. Crystal structures have been determined by powder XRD and optimized by DFT calculations to evaluate the strength of the dihydrogen bonds. Sr(NH3)(BH4)2 (Pbcn) and Sr(NH3)2(BH4)2 (Pnc2) are layered structures, whereas M(NH3)4(BH4)2 (M=Ca and Sr; P21/c) are molecular structures connected by dihydrogen bonds. Both series of compounds release NH3 gas upon thermal treatment if the partial pressure of ammonia is low. Therefore, the strength of the dihydrogen bonds, the structure of the compounds, and the NH3/BH4− ratio for M(NH3)n(BH4)m have little influence on the composition of the released gasses. The composition of the released gas depends mainly on the thermal stability of the ammine metal borohydride and the corresponding metal borohydride.
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Sep 2015
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