468 research outputs found
Powder diffraction methods for studies of borohydride-based energy storage materials
The world today is facing increasing energy demands and a simultaneous demand for cleaner and more environmentally friendly energy technologies. Hydrogen is recognized as a possible renewable energy carrier, but its large-scale utilization is mainly hampered by insufficient hydrogen storage capabilities. In this scenario, powder diffraction has a central position as the most informative and versatile technique available in materials science. This is illustrated in the present review by synthesis, physical, chemical and structural characterisation of novel boron based hydrides for hydrogen storage. Numerous novel BH4- based materials have been investigated during the past few years and this class of materials has a fascinating structural chemistry. The experimental methods presented can be applied to a variety of other material
Sr3CrN3: a new electride with partially filled d-shells
Electrides are ionic crystals in which the electrons prefer to occupy free
space, serving as anions. Because the electrons prefer to be in the pockets,
channels, or layers to the atomic orbitals around the nuclei, it has been
challenging to find electrides with partially filled d-shells, since an
unoccupied d-shell provides an energetically favourable location for the
electrons to occupy. We recently predicted the existence of electrides with
partially filled d-shells using high-throughput computational screening. Here,
we provide an experimental support using X-ray absorption spectroscopy and
X-ray and neutron diffraction to show that Sr3CrN3 is indeed an electride
despite its partial d-shell configuration. Our findings indicate that Sr3CrN3
is the first known electride with a partially filled d-shell, in agreement with
theory, which significantly broadens the criteria for the search for new
electride materials
High-pressure phase and transition phenomena in ammonia borane NH3BH3 from X-ray diffraction, Landau theory, and ab initio calculations
Structural evolution of a prospective hydrogen storage material, ammonia
borane NH3BH3, has been studied at high pressures up to 12 GPa and at low
temperatures by synchrotron powder diffraction. At 293 K and above 1.1 GPa a
disordered I4mm structure reversibly transforms into a new ordered phase. Its
Cmc21 structure was solved from the diffraction data, the positions of N and B
atoms and the orientation of NH3 and BH3 groups were finally assigned with the
help of density functional theory calculations. Group-theoretical analysis
identifies a single two-component order parameter, combining ordering and
atomic displacement mechanisms, which link an orientationally disordered parent
phase I4mm with ordered distorted Cmc21, Pmn21 and P21 structures. We propose a
generic phase diagram for NH3BH3, mapping three experimentally found and one
predicted (P21) phases as a function of temperature and pressure, along with
the evolution of the corresponding structural distortions. Ammonia borane
belongs to the class of improper ferroelastics and we show that both
temperature- and pressure-induced phase transitions can be driven to be of the
second order. The role of N-H...H-B dihydrogen bonds and other intermolecular
interactions in the stability of NH3BH3 polymorphs is examined.Comment: 23 pages, 7 figure
Synthesis of a Bimetallic Dodecaborate LiNaB_(12)H_(12)with Outstanding Superionic Conductivity
Metal dodecaborates M_2/_nB_(12)H_(12) (n denotes the valence of
the metal M), containing icosahedral polyatomic anion
[B_(12)H_(12)]^(2â), have been attracting increasing interest as potential
energy materials, especially in the context of hydrogen
storage and superionic conductivity. M_2/_nB_(12)H_(12) are
commonly formed as dehydrogenation intermediates from
metal borohydrides M(BH_4)_n, like LiBH_4 and Mg(BH_4)_2,
which are well-known as potential high-density hydrogen
storage materials. The strong BâB bond in the icosahedral
[B_(12)H_(12)]^(2â), however, is regarded to be the key factor that
prevents the rehydrogenation of dodecaborates. In order to
elucidate the mechanism as well as to provide effective
solutions to this problem, a novel solvent-free synthesis route
of anhydrous M_2/nB_(12)H_(12) (here M means Li, Na, and K) has
been developed. Thermal stability and transformations of the
anhydrous single phase Li_2B_(12)H_(12) suggested the formation of
the high temperature polymorph of Li_2B_(12)H_(12) during the
dehydrogenation of LiBH_4, while concurrently emphasized the
importance of further investigation on the decomposition
mechanism of metal borohydrides and metal dodecaborates.
The high stability of icosahedral [B_(12)H_(12)]^(2â), on the other hand,
favors its potential application as solid electrolyte. Recently,
Na^+ conductivity of Na_2B_(12)H_(12) was reported to be 0.1 S/cm
above its orderâdisorder phase transition at âź529 K, which is
comparable to that of a polycrystalline βâ-Al_2O_3 (0.24 S/cm at
573 K) solid state Na-electrolyte. Mechanistic understanding
on the diffusion behavior of cation and further improvement of
ionic conductivity at a lower temperature, however, are
important in order to facilitate the practical application of
metal dodecaborates as superionic conductors
Transformation of a Chiral Nanoporous Bimetallic Cyano-Bridged Framework Triggered by Dehydration/Rehydration
Exploring polymorphism and stoichiometric diversity in naproxen/proline cocrystals
We present naproxen/proline cocrystals discovered when combining enantiopure and racemic naproxen and proline. Using liquid-assisted grinding as the main method to explore the variety of crystal forms in this system, we found 17 cocrystals, of which the structures of only four of them were previously known. The naproxen/proline system exhibited multiple polymorphs of 1â:â1 stoichiometry as well as more rare cocrystals with 1â:â2 and 2â:â3 stoichiometries, two cocrystal hydrates and one cocrystal solvate. In situ ball-milling, used to monitor liquid-assisted grinding reactions, revealed that the solvent dictates the reaction intermediates even if the final reaction product stays the same. Synchrotron X-ray diffraction data collected in situ upon heating allowed us to monitor directly the phase changes upon heating and gave access to pure diffraction patterns of several cocrystals, thus enabling their structure determination from powder X-ray diffraction data; this method also confirmed the formation of a conglomerate in the RS-naproxen/DL-proline system. Proline in cocrystals kept its ability to form charge-assisted head-to-tail NâHâŻO hydrogen bonds, typical of pure crystalline amino acids, thus increasing the percentage of strong charge-assisted interactions in the structure and consequently providing some of the cocrystals with higher melting points as compared to pure naproxen. The majority of drugs are chiral, and hence, these data are of importance to the pharmaceutical industry as they provide insight into the challenges of chiral cocrystallization
A New Family of Bimetallic Framework Materials Showing Reversible Structural Transformations
Versatile in situ powder X-ray diffraction cells for solidâgas investigations
Two multipurpose sample cells of quartz (SiO2) or sapphire (Al2O3) capillaries, developed for the study of solidâgas reactions in dosing or flow mode, are presented. They allow fast change of pressure up to 100 or 300â
bar (1â
bar = 100â
000â
Pa) and can also handle solidâliquidâgas studies
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