Abstract
M
n+1
AX
n
phases are a large family of compounds that have been limited, so far, to carbides and nitrides. Here we report the prediction of a compound, Ti
2
InB
2
, a stable boron-based ...ternary phase in the Ti-In-B system, using a computational structure search strategy. This predicted Ti
2
InB
2
compound is successfully synthesized using a solid-state reaction route and its space group is confirmed as
P
$$\bar 6$$
6
¯
m2
(No. 187), which is in fact a hexagonal subgroup of
P6
3
/mmc
(No. 194), the symmetry group of conventional M
n+1
AX
n
phases. Moreover, a strategy for the synthesis of MXenes from M
n+1
AX
n
phases is applied, and a layered boride, TiB, is obtained by the removal of the indium layer through dealloying of the parent Ti
2
InB
2
at high temperature under a high vacuum. We theoretically demonstrate that the TiB single layer exhibits superior potential as an anode material for Li/Na ion batteries than conventional carbide MXenes such as Ti
3
C
2
.
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•Hybrid approach enables modeling of long-range diffusion in non-crystalline materials.•Coordination polymer design maximizes Zn2+ coordination with phosphoric acid.•Proton ...conductivity in proposed coordination polymers reaches 0.4Scm−1 at 125 °C.•Activation energy for proton diffusion is below 0.1 eV.
Fast proton conductors are important materials for catalysis and energy conversion applications. The glassy coordination polymers are an important class of proton conductors due to their good mechanical moldability; however, their conductivity has been limited to ca. 10 mS cm−1 at 100 °C. The systematic design of coordination polymers with fast proton conduction requires an atomistic simulation method that can describe long-range proton diffusion within an affordable computational time. The methodologies of atomistic simulations are separately limited and cannot fairly describe the long-range proton conduction in non-crystalline materials. In this work, we develop a hybrid approach that combines the molecular dynamics based on a conventional force-field and the kinetic Monte Carlo method, which allows for the large-scale (thousands of atoms) and long time (few nanoseconds) simulation of the long-range ionic diffusion in non-crystalline materials. Based on the developed approach, we propose and confirm a design concept for a fast proton-conducting coordination polymer based on Zn2+ ions and phosphoric acid.
Fast ionic conductors have considerable potential to enable technological development for energy storage and conversion. Hydride (H
) ions are a unique species because of their natural abundance, ...light mass, and large polarizability. Herein, we investigate characteristic H
conduction, i.e., fast ionic conduction controlled by a pre-exponential factor. Oxygen-doped LaH
(LaH
O
) has an optimum ionic conductivity of 2.6 × 10
S cm
, which to the best of our knowledge is the highest H
conductivity reported to date at intermediate temperatures. With increasing oxygen content, the relatively high activation energy remains unchanged, whereas the pre-exponential factor decreases dramatically. This extraordinarily large pre-exponential factor is explained by introducing temperature-dependent enthalpy, derived from H
trapped by lanthanum ions bonded to oxygen ions. Consequently, light mass and large polarizability of H
, and the framework comprising densely packed H
in LaH
O
are crucial factors that impose significant temperature dependence on the potential energy and implement characteristic fast H
conduction.
Further attenuation of Rayleigh scattering of silica glass is required to extend the capacity of long‐distance optical fiber communication. To theoretically examine the effect of aluminum and ...fluorine co‐doping on the density fluctuations of silica glass, which is related to Rayleigh scattering, a set of force‐matching potentials (FMP) for simulating F‐doped aluminosilicates was developed using Bayesian optimization based on density functional theory calculations. Molecular dynamics (MD) simulations with the new FMP could evaluate the densities of silica glasses to which a small amount of fluorine was doped and those of aluminosilicate glasses with a wide range of aluminum contents within reasonable accuracy. The FMP successfully represents the changing role of aluminum from a network former without a compensating cation (threefold coordination) to that with a compensating cation and a charge compensator in the aluminosilicates. Indeed, relative concentrations of four, five, and sixfold‐coordinated aluminum observed by NMR measurements were reproduced better than the original Teter potential at a high aluminum content. At an aluminum content lower than 1 mol%, threefold‐coordinated aluminum was observed, which is consistent with ESR measurements. After careful validations of the FMP, the effect of the co‐doping of alumina and fluorine on the density fluctuations of silica glass was computationally examined. Consequently, it was expected that the co‐doping might not sufficiently attenuate the Rayleigh scattering, even though 1 wt% fluorine would be able to reduce the density fluctuations of aluminosilicate glasses for some extent. This is because more alumina‐doping increases density fluctuations of silica glass if the drawing temperature and procedure are the same with those for silica glass fiber. Thereby, a possible fabrication process to sufficiently attenuate the Rayleigh scattering of the F‐doped aluminosilicate glass was proposed, according to the density fluctuation analysis at high temperature.
A low‐temperature ammonia synthesis process is required for on‐site synthesis. Barium‐doped calcium amide (Ba‐Ca(NH2)2) enhances the efficacy of ammonia synthesis mediated by Ru and Co by 2 orders of ...magnitude more than that of a conventional Ru catalyst at temperatures below 300 °C. Furthermore, the presented catalysts are superior to the wüstite‐based Fe catalyst, which is known as a highly active industrial catalyst at low temperatures and pressures. Nanosized Ru–Ba core–shell structures are self‐organized on the Ba‐Ca(NH2)2 support during H2 pretreatment, and the support material is simultaneously converted into a mesoporous structure with a high surface area (>100 m2 g−1). These self‐organized nanostructures account for the high catalytic performance in low‐temperature ammonia synthesis.
Ruthenium–barium core–shell nanoparticles and a mesoporous calcium amide matrix (Ru/Ba‐Ca(NH2)2) self‐organize during treatment with hydrogen gas. The resultant composite material presents much higher catalytic performance in low‐temperature ammonia synthesis than other ruthenium catalysts and an industrial iron catalyst.
Transparent silica glass is an indispensable material for today's information technology society as an ultra-low loss optical fiber. Recently, further low-loss optical fibers are demanded due to ...rapidly expanding information. A small amount of fluorine doping is known to reduce the Rayleigh scattering further by reducing the density fluctuations of silica glass, even though the fluorine is an impurity for the pristine silica glass. This study devoted to answer the riddle of F-doping and an accurate force-matching potential optimized by machine-learning enables us to understand how fluorine remedies the disorders in silica glass. It was found that fluorine mainly replaces an oxygen in tetrahedral SiO4 unit, but also forms five-fold Si, such as SiO4F and SiO3F2 units. The former disrupts silica network, while the latter attenuates the network rigidity by loosening the five Si-O(F) bonds. Since the two local effects of fluorine spreads through the glass network, F-doping prompts silica glass to relax further even at temperature lower than the glass transition (fictive) temperature. Consequently, fluorine minimizes the density fluctuation (thus, Rayleigh scattering) of silica glass at around 1 wt%, although fluorine itself is an impurity for silica glass.
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•Accurate force-matching potential for F-doped silica was developed based on DFT calculations using Bayesian optimization.•The new potential successfully reproduced anomaly of density change of silica and effect of F-doping to anomaly attenuation.•Large-scale MD simulations unraveled how fluorine minimizes density fluctuation of silica glass.
The efficient reduction of atmospheric nitrogen to ammonia under low pressure and temperature conditions has been a challenge in meeting the rapidly increasing demand for fertilizers and hydrogen ...storage. Here, we report that Ca
N:e
, a two-dimensional electride, combined with ruthenium nanoparticles (Ru/Ca
N:e
) exhibits efficient and stable catalytic activity down to 200 °C. This catalytic performance is due to Ca
N
·e
H
formed by a reversible reaction of an anionic electron with hydrogen (Ca
N:e
+
H ↔ Ca
N
·e
H
) during ammonia synthesis. The simplest hydride, CaH
, with Ru also exhibits catalytic performance comparable to Ru/Ca
N:e
. The resultant electrons in these hydrides have a low work function of 2.3 eV, which facilitates the cleavage of N
molecules. The smooth reversible exchangeability between anionic electrons and H
ions in hydrides at low temperatures suppresses hydrogen poisoning of the Ru surfaces. The present work demonstrates the high potential of metal hydrides as efficient promoters for low-temperature ammonia synthesis.
Suzuki cross-coupling reactions catalyzed by palladium are powerful tools for the synthesis of functional organic compounds. Excellent catalytic activity and stability require negatively charged Pd ...species and the avoidance of metal leaching or clustering in a heterogeneous system. Here we report a Pd-based electride material, Y
Pd
, in which active Pd atoms are incorporated in a lattice together with Y. As evidenced from detailed characterization and density functional theory (DFT) calculations, Y
Pd
realizes negatively charged Pd species, a low work function and a high carrier density, which are expected to be beneficial for the efficient Suzuki coupling reaction of activated aryl halides with various coupling partners under mild conditions. The catalytic activity of Y
Pd
is ten times higher than that of pure Pd and the activation energy is lower by nearly 35%. The Y
Pd
intermetallic electride catalyst also exhibited extremely good catalytic stability during long-term coupling reactions.
Control of charge carriers that transport through the molecular junctions is essential for thermoelectric materials. In general, the charge carrier depends on the dominant conduction orbitals and is ...dominantly determined by the terminal anchor groups. The present study discloses the synthesis, physical properties in solution, and single-molecule conductance of paddle-wheel diruthenium complexes
1
R
having diarylformamidinato supporting ligands (DArF:
p
-R-C
6
H
4
-NCHN-C
6
H
4
-R-
p
) and two axial thioanisylethynyl conducting anchor groups, revealing unique substituent effects with respect to the conduction orbitals. The complexes
1
R
with a few different aryl substituents (R = OMe, H, Cl, and CF
3
) were fully characterized by spectroscopic and crystallographic analyses. The single-molecule conductance determined by the scanning tunneling microscope break junction (STM-BJ) technique was in the 10
−5
to 10
−4
G
0
region, and the order of conductance was
1
OMe
>
1
CF3
>
1
H
∼
1
Cl
, which was not consistent with the Hammett substituent constants
σ
of R. Cyclic voltammetry revealed the narrow HOMO-LUMO gaps of
1
R
originating from the diruthenium motif, as further supported by the DFT study. The DFT-NEGF analysis of this unique result revealed that the dominant conductance routes changed from HOMO conductance (for
1
OMe
) to LUMO conductance (for
1
CF3
). The drastic change in the conductance properties originates from the intrinsic narrow HOMO-LUMO gaps.
Dominant conduction orbitals of paddle-wheel organodiruthenium complexes can be facilely controlled by the substituents embedded in the amidinato ligands.
Here, we report multinuclear organometallic molecular wires having (2,5-diethynylthiophene)diyl-Ru(dppe)
2
repeating units. Despite the molecular dimensions of 2-4 nm the multinuclear wires show high ...conductance (up to 10
−2
to 10
−3
G
0
) at the single-molecule level with small attenuation factors (
β
) as revealed by STM-break junction measurements. The high performance can be attributed to the efficient energy alignment between the Fermi level of the metal electrodes and the HOMO levels of the multinuclear molecular wires as revealed by DFT-NEGF calculations. Electrochemical and DFT studies reveal that the strong Ru-Ru interaction through the bridging ligands raises the HOMO levels to access the Fermi level, leading to high conductance and small
β
values.
Multinuclear organometallic molecular wires having (diethynylthiophene)diyl-Ru(dppe)
2
repeating units show high conductance with small attenuation factors. The strong Ru-Ru interaction is the key for the long-range carrier transport.
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