147 research outputs found
First-principles study on the intermediate compounds of LiBH
We report the results of the first-principles calculation on the intermediate
compounds of LiBH. The stability of LiBH and LiBH has been examined with the ultrasoft pseudopotential method based on
the density functional theory. Theoretical prediction has suggested that
monoclinic LiBH is the most stable among the candidate
materials. We propose the following hydriding/dehydriding process of LiBH
via this intermediate compound : LiBHLiBH LiH HLiH B H. The hydrogen content and enthalpy of the first
reaction are estimated to be 10 mass% and 56 kJ/mol H, respectively, and
those of the second reaction are 4 mass% and 125 kJ/mol H. They are in good
agreement with experimental results of the thermal desorption spectra of
LiBH. Our calculation has predicted that the bending modes for the
-phonon frequencies of monoclinic LiBH are lower than
that of LiBH, while stretching modes are higher. These results are very
useful for the experimental search and identification of possible intermediate
compounds.Comment: 7 pages, 5 figures, submitted to PR
Development of complex hydrides for fast ionic conduction
Complex hydrides have been attracting much attention as solid-state fast ionic conductors since we reported the fast lithium ionic conduction in LiBH4 [1]. The development of fast ionic conductors is important because of their potential applications as solid electrolytes in rechargeable batteries [2]. We have worked on the development of lithium ionic conductors as well as sodium ionic conductors of complex hydrides.
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Topological Data Analysis of Ion Migration Mechanism
Topological data analysis based on persistent homology has been applied to
the molecular dynamics simulation for the fast ion-conducting phase
(-phase) of AgI, to show its effectiveness on the ion-migration
mechanism analysis.Time-averaged persistence diagrams of -AgI, which
quantitatively records the shape and size of the ring structures in the given
atomic configurations, clearly showed the emergence of the four-membered rings
formed by two Ag and two I ions at high temperatures. They were identified as
common structures during the Ag ion migration. The averaged potential energy
change due to the deformation of four-membered ring during Ag migration agrees
well with the activation energy calculated from the conductivity Arrhenius
plot. The concerted motion of two Ag ions via the four-membered ring was also
successfully extracted from molecular dynamics simulations by our approach,
providing the new insight into the specific mechanism of the concerted motion.Comment: 8 pages, 7 figure
Magnetic Phase Transition of MnBi under High Magnetic Fields and High Temperature
Magnetization measurements and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in magnetic fields up to 14 T and in 300-773 K, in order to investigate the magnetic phase transition. The magnetic phase transition temperature (T t ) at a zero magnetic field is 628 K and linearly increases with increasing fields up to 14 T at the rate of 2 KT À1 . A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above T t . The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in 626-623 K, which relates to the metamagnetic transition. The obtained results were discussed on the basis of a mean field theory
NMR Studies of Lithium Diffusion in Li3(NH2)2I over Wide Range of Li+ Jump Rates
We have studied the Li diffusion in the complex hydride Li3(NH2)2I which appears to exhibit fast Li ion conduction. To get a detailed insight into the Li motion, we have applied 7Li nuclear magnetic resonance spectroscopy methods, such as spin-lattice relaxation in the laboratory and rotating frames of reference, as well as spin-alignment echo. This combined approach allows us to probe Li jump rates over the wide dynamic range (~102–109 s−1). The spin-lattice relaxation data in the range 210–410 K can be interpreted in terms of a thermally-activated Li jump process with a certain distribution of activation energies. However, the low-temperature spin-alignment echo decays at T≤200 K suggest the presence of another Li jump process with the very low effective activation energy. © 2017 Walter de Gruyter GmbH, Berlin/Boston 2017
Colossal reversible barocaloric effects in a plastic crystal mediated by lattice vibrations and ion diffusion
Solid-state methods for cooling and heating promise a more sustainable
alternative to current compression cycles of greenhouse gases and inefficient
fuel-burning heaters. Barocaloric effects (BCE) driven by hydrostatic pressure
() are especially encouraging in terms of large adiabatic temperature
changes ( K) and colossal isothermal entropy changes
( JKkg). However, BCE typically require
large pressure shifts due to irreversibility issues, and sizeable
and seldom are realized in a same material. Here, we demonstrate
the existence of colossal and reversible BCE in LiCBH, a
well-known solid electrolyte, near its order-disorder phase transition at
K. Specifically, for GPa we
measured JKkg and K, which individually rival with state-of-the-art
barocaloric shifts obtained under similar pressure conditions. Furthermore,
over a wide temperature range, pressure shifts of the order of GPa yield
huge reversible barocaloric strengths of
JKkgMPa. Molecular dynamics simulations were carried out
to quantify the role of lattice vibrations, molecular reorientations and ion
diffusion on the disclosed colossal BCE. Interestingly, lattice vibrations were
found to contribute the most to while the diffusion of lithium
ions, despite adding up only slightly to the accompanying entropy change, was
crucial in enabling the molecular order-disorder phase transition. Our work
expands the knowledge on plastic crystals and should motivate the investigation
of BCE in a variety of solid electrolytes displaying ion diffusion and
concomitant molecular orientational disorder.Comment: 13 pages, 7 figure
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