High-pressure phase ofNaBH4: Crystal structure from synchrotron powder diffraction data (original) (raw)
Related papers
An extended high pressure-temperature phase diagram of NaBH[sub 4]
The Journal of Chemical Physics, 2009
We have studied the structural stability of NaBH 4 under pressures up to 17 GPa and temperatures up to 673 K in a diamond anvil cell and formed an extended high P-T phase diagram using combined synchrotron x-ray diffraction and Raman spectroscopy. Even though few reports on phase diagram of NaBH 4 are found in current literature, up to our knowledge this is the first experimental work using diamond anvil cell in a wide pressure/temperature range. Bulk modulus, its temperature dependence, and thermal expansion coefficient for the ambient cubic phase of NaBH 4 are found to be 18.76͑1͒ GPa, −0.0131 GPa K −1 , and 12.5ϫ 10 −5 + 23.2ϫ 10 −8 T / K, respectively. We have also carried out Raman spectroscopic studies at room temperature up to 30 GPa to reinvestigate the phase transitions observed for NaBH 4 . A comparative symmetry analysis also has been carried out for different phases of NaBH 4 . Physics 131, 074505-1 074505-2 George et al. J. Chem. Phys. 131, 074505 ͑2009͒ 074505-3 Sodium borohydride J. Chem. Phys. 131, 074505 ͑2009͒ 074505-5 Sodium borohydride J. Chem. Phys. 131, 074505 ͑2009͒
High‐pressure phase transitions in NaBH4 from first‐principles calculations
physica status solidi (b), 2011
We present a study on NaBH4 under high pressure by using the ab initio pseudopotential plane‐wave method. The calculations show that a structural phase transition takes place at 10.91 GPa from the β‐NaBH4 structure (tetragonal‐$P{\bar {4}}{\rm 2}_{{\rm 1}} c$) to the γ‐NaBH4 structure (orthorhombic‐Pnma). Band‐structure calculation reveals that the two phases show an insulator behaviour with a finite energy gap. There is no pressure‐induced softening behaviour from our calculated phonon dispersion curves near the phase transition pressure. We also characterize charge transfer and Mulliken population analyses of these structures. The Mulliken population analyses indicate that the β‐NaBH4 phase is expected to be the most promising candidate for hydrogen storage.
Physical Review B, 2008
An in situ combined high-temperature high-pressure synchrotron radiation diffraction study has been carried out on LiBH 4 . The phase diagram of LiBH 4 is mapped to 10 GPa and 500 K, and four phases are identified. The corresponding structural distortions are analyzed in terms of symmetry-breaking atomic position shifts and anion ordering. Group-theoretical and crystal-chemical considerations reveal a nontrivial layered structure of LiBH 4 . The layers and their deformations define the structural stability of the observed phases.
Pressure induced structural transitions in the potential hydrogen storage compound NH3BH3
Ammonia borane has received much attention in recent years as it is reported to have up to 19.6 wt % of hydrogen [1-2]. Hydrogen is released in a three step process when heated above 100^oC. To understand the structural stability of this compound under compression, we have performed high pressure angle dispersive x-ray diffraction experiments up to 27 GPa using synchrotron x-rays at HPCAT, Advanced Photon Source. Two successive pressure induced structural phase transitions were observed. The ambient tetragonal structure transforms to an orthorhombic structure around 1.2 GPa and then to another high pressure phase above 8 GPa. Complementary neutron diffraction experiments performed up to 5 GPa at LANSCE are in good agreement with the x-ray results. The structural details of the high pressure phases will be presented.[4pt] [1] Z. Xiong et al., Nature, 7 (2008) pp 034508[0pt] [2] J.B.Yang etal., Appl.Phys.Lett, 92 (2008) pp 091916
High-Pressure Polymorphism as a Step towards Destabilization of LiBH4
Angewandte Chemie International Edition, 2008
Lithium borohydride could be an extremely efficient energy storage system containing 18.5 wt % hydrogen. However, owing to its high thermal stability, it is not yet regarded as a practical H-storage material. More experimental and theoretical efforts are required to improve the hydrogen-storage properties of this compound. Experimental investigations of light metal borohydrides such as LiBH 4 are difficult owing to the weak diffracting power of the light elements for X-ray diffraction and to considerable incoherent scattering by H and high absorption by natural B and Li for neutron diffraction. For these reasons, LiBH 4 has been extensively studied theoretically by "first-principles" methods based on density functional theory (DFT). A large amount of information has been generated, including possible crystal and electronic structures, lattice dynamics, surface properties, decomposition mechanisms, and intermediate products. Surprisingly, theory and experiment agreed only on the symmetry of the room-temperature, ambient-pressure polymorph of lithium borohydride. Despite the fact that the temperature-induced structural transition in LiBH 4 has been known for a long time, the experimental structural data on the high-temperature form have not yet been confirmed by theory. In particular, the presumed hexagonal P6 3 mc structure, first suggested from diffraction experiments, was found to have a relatively high energy and imaginary vibrational frequencies. Other calculations have also shown that the P6 3 mc structure is rather unstable. The same problem holds for the pressure evolution of LiBH 4 ; a phase transition below 5 GPa was identified more than 30 years ago, but there is still no agreement on the structure of the high-pressure phase. Theoretical predictions suggest a cubic NaBH 4 -type structure above 6.2 GPa, a monoclinic P2 1 /c structure at approximately 1 GPa, and a monoclinic Cc structure above 2.2 GPa (3 GPa in reference [4]). However, the most recent experimental study of LiBH 4 at pressures up to 9 GPa concludes that none of these predictions are correct, although the structure of the highpressure polymorph itself could not be identified, owing to experimental limitations. Thus, the first efforts in understanding the material properties, both experimental and theoretical, were discouraging. Both the pressure and temperature evolution of the corresponding structure have found no consistent explanation in the framework of "first-principles" theories.
Journal of Alloys and Compounds, 2011
The structural, electronic, mechanical properties and hardness of orthorhombic B 28 and tetragonal B 48 boron phases have been studied by first-principles of pseudopotential calculations. The results indicated that both boron phases are energetically and also mechanically stable. In addition to electronic properties of highly directional covalent bonds, mechanical properties, and also the Debye temperatures of structures support that both are superhard materials. Calculated electronic band structures and density of states revealed that orthorhombic B 28 crystal is a semiconductor, and the tetragonal B 48 is metallic. The pressure-dependent behaviors of both structures are different, and both are ultra-incompressible and anisotropic materials. The physical parameters of the structures such as lattice parameters, bond lengths, and also energy gaps between valance and conduction bands are closely sensitive to applied external pressures. By means of pressure-volume graphs, obtained EOSs for ␣-rhombohedral B 12 , orthorhombic B 28 and tetragonal B 48 boron phases are compared with available data. However, energetically possible pressure-induced phase transitions among the purposed structures are predicted on the pressure range of 0-460 GPa. Furthermore, our calculations showed that for the pressures from 0 GPa to 24 GPa energetically the more stable elemental boron phase is ␣-rhombohedral B 12 , and from 24 GPa to 106 GPa is orthorhombic B 28 , and from 106 GPa to 460 GPa is ␣-Ga-type boron.
High pressure study on structural and vibrational properties of NH 3 BH 3
Journal of Physics: Conference Series, 2012
The structural and vibrational properties of potential hydrogen storage compound NH 3 BH 3 have been studied through density functional theory at ambient as well as high pressures upto 10 GPa. The calculated lattice parameters at ambient pressure are in good agreement with experiments. The compressibility of NH 3 BH 3 along the crystallographic a-axis is almost constant when compared to b-and c-axes, which is an indication of anisotropic compressibility. The zone center vibrational frequencies of NH 3 BH 3 at ambient and 10 GPa pressures are calculated. The A 2 and B 1 symmetry modes are independent of pressure, whereas the A 1 symmetry modes increases and B 2 symmetry modes decreases with pressure.
Structure and Properties of NaBH 4 ·2H 2 O and NaBH 4
European Journal of Inorganic Chemistry, 2008
NaBH 4 ·2H 2 O and NaBH 4 were studied by single-crystal Xray diffraction and vibrational spectroscopy. In NaBH 4 ·2H 2 O, the BH 4 anion has a nearly ideal tetrahedral geometry and is bridged with two Na + ions through the tetrahedral edges. The structure does not contain classical hydrogen bonds, but reveals strong dihydrogen bonds of 1.77-1.95 Å. Crystal structures and vibrational spectra of NaBr·2H 2 O and Eur.
Physics and Chemistry of Minerals, 2007
A single-crystal sample of galenobismutite was subjected to hydrostatic pressures in the range of 0.0001 and 9 GPa at room temperature using the diamond-anvil cell technique. A series of X-ray diVraction intensities were collected at ten distinct pressures using a CCD equipped 4-circle diVractometer. The crystal structure was reWned to R1(|F 0 | > 4 ) values of approximately 0.05 at all pressures. By Wtting a third-order Birch-Murnaghan equation of state to the unit-cell volumes V 0 = 700.6(2) Å 3 , K 0 = 43.9(7) GPa and dK/dP = 6.9(3) could be determined for the lattice compression. Both types of cations in galenobismutite have stereochemically active lone electron pairs, which distort the cation polyhedra at room pressure. The cation eccentricities decrease at higher pressure but are still pronounced at 9 GPa. Galenobismutite is isotypic with CaFe 2 O 4 (CF) but moves away from the idealised CF-type structure during compression. Instead of the two octahedral cation sites and one bi-capped trigonal-prismatic site, PbBi 2 S 4 attains a new high-pressure structure characterised by one octahedral site and two mono-capped trigonal-prismatic sites. Analyses of the crystal structure at high pressure conWrm the preference of Bi for the octahedral site and the smaller one of the two trigonal-prismatic sites.