The discovery of superconductivity in H3S at 203 K marked an advance towards room‐temperature superconductivity and demonstrated the potential of H‐dominated compounds to possess a high critical ...temperature (Tc). There have been numerous reports of the H‐S system over the last five years, but important questions remain unanswered. It is crucial to verify whether the Tc was determined correctly for samples prepared from compressed H2S, since they are inevitably contaminated with H‐depleted byproducts. Here, we prepare stoichiometric H3S by direct in situ synthesis from elemental S and excess H2. The Im3‾
m phase of D3S samples exhibits a Tc significantly higher than previously reported values (ca. 150 K), reaching a maximum Tc of 166 K at 157 GPa. Furthermore, we confirm that the sharp decrease in Tc below 150 GPa is accompanied by continuous rhombohedral structural distortions and demonstrate that the Cccm phase is non‐metallic, with molecular H2 units in the crystal structure.
The Im3‾m
phase of stoichiometric D3S, synthesized from elemental S and excess D2 in a diamond anvil cell, exhibits superconductivity with Tc of 166 K at 157 GPa. This is significantly higher than previously reported circa 150 K for samples prepared from disproportionated D2S.
We investigated the structure of SiO₂ glass up to 172 GPa using high-energy X-ray diffraction. The combination of a multichannel collimator with diamond anvil cells enabled the measurement of ...structural changes in silica glass with total X-ray diffraction to previously unachievable pressures. We show that SiO₂ first undergoes a change in Si–O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. Si–O bond length shows first an increase due to the fourfold to sixfold coordination change and then a smaller linear decrease up to 172 GPa. We reconcile the changes in relation to the oxygen-packing fraction, showing that oxygen packing decreases at ultrahigh pressures to accommodate the higher than sixfold Si–O coordination. These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures.
Most of the studied two-dimensional (2D) materials are based on highly symmetric hexagonal structural motifs. In contrast, lower-symmetry structures may have exciting anisotropic properties leading ...to various applications in nanoelectronics. In this work we report the synthesis of nickel diazenide NiN2 which possesses atomic-thick layers comprised of Ni2N3 pentagons forming Cairo-type tessellation. The layers of NiN2 are weakly bonded with the calculated exfoliation energy of 0.72 J/m2, which is just slightly larger than that of graphene. The compound crystallizes in the space group of the ideal Cairo tiling (P4/mbm) and possesses significant anisotropy of elastic properties. The single-layer NiN2 is a direct-band-gap semiconductor, while the bulk material is metallic. This indicates the promise of NiN2 to be a precursor of a pentagonal 2D material with a tunable direct band gap.
Abstract
Hydrogen-rich superhydrides are believed to be very promising high-
T
c
superconductors. Recent experiments discovered superhydrides at very high pressures, e.g. FeH
5
at 130 GPa and LaH
10
...at 170 GPa. With the motivation of discovering new hydrogen-rich high-
T
c
superconductors at lowest possible pressure, here we report the prediction and experimental synthesis of cerium superhydride CeH
9
at 80–100 GPa in the laser-heated diamond anvil cell coupled with synchrotron X-ray diffraction. Ab initio calculations were carried out to evaluate the detailed chemistry of the Ce-H system and to understand the structure, stability and superconductivity of CeH
9
. CeH
9
crystallizes in a
P6
3
/mmc
clathrate structure with a very dense 3-dimensional atomic hydrogen sublattice at 100 GPa. These findings shed a significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range. Discovery of superhydride CeH
9
provides a practical platform to further investigate and understand conventional superconductivity in hydrogen rich superhydrides.
Abstract
Following the discovery of high-temperature superconductivity in the La–H system, we studied the formation of new chemical compounds in the barium-hydrogen system at pressures from 75 to 173 ...GPa. Using in situ generation of hydrogen from NH
3
BH
3
, we synthesized previously unknown superhydride BaH
12
with a pseudocubic (
fcc
) Ba sublattice in four independent experiments. Density functional theory calculations indicate close agreement between the theoretical and experimental equations of state. In addition, we identified previously known
P
6
/mmm
-BaH
2
and possibly BaH
10
and BaH
6
as impurities in the samples. Ab initio calculations show that newly discovered semimetallic BaH
12
contains H
2
and H
3
–
molecular units and detached H
12
chains which are formed as a result of a Peierls-type distortion of the cubic cage structure. Barium dodecahydride is a unique molecular hydride with metallic conductivity that demonstrates the superconducting transition around 20 K at 140 GPa.
Abstract
The possibility of high, room-temperature superconductivity was predicted for metallic hydrogen in the 1960s. However, metallization and superconductivity of hydrogen are yet to be ...unambiguously demonstrated and may require pressures as high as 5 million atmospheres. Rare earth based “superhydrides”, such as LaH
10
, can be considered as a close approximation of metallic hydrogen even though they form at moderately lower pressures. In superhydrides the predominance of H-H metallic bonds and high superconducting transition temperatures bear the hallmarks of metallic hydrogen. Still, experimental studies revealing the key factors controlling their superconductivity are scarce. Here, we report the pressure and magnetic field dependence of the superconducting order observed in LaH
10
. We determine that the high-symmetry high-temperature superconducting
Fm-3m
phase of LaH
10
can be stabilized at substantially lower pressures than previously thought. We find a remarkable correlation between superconductivity and a structural instability indicating that lattice vibrations, responsible for the monoclinic structural distortions in LaH
10
, strongly affect the superconducting coupling.
Tailoring nanoarchitecture of materials offers unprecedented opportunities in utilization of their functional properties. Nanostructures of vanadium oxide, synthesized by electrochemical deposition, ...are studied as a cathode material for rechargeable Na-ion batteries. Ex situ and in situ synchrotron characterizations revealed the presence of an electrochemically responsive bilayered structure with adjustable intralayer spacing that accommodates intercalation of Na+ ions. Sodium intake induces organization of overall structure with appearance of both long- and short-range order, while deintercalation is accompanied with the loss of long-range order, whereas short-range order is preserved. Nanostructured electrodes achieve theoretical reversible capacity for Na2V2O5 stochiometry of 250 mAh/g. The stability evaluation during charge–discharge cycles at room temperature revealed an efficient 3 V cathode material with superb performance: energy density of ∼760 Wh/kg and power density of 1200 W/kg. These results demonstrate feasibility of development of the ambient temperature Na-ion rechargeable batteries by employment of electrodes with tailored nanoarchitectures.
Material design in terms of their morphologies other than solid nanoparticles can lead to more advanced properties. At the example of iron oxide, we explored the electrochemical properties of hollow ...nanoparticles with an application as a cathode and anode. Such nanoparticles contain very high concentration of cation vacancies that can be efficiently utilized for reversible Li ion intercalation without structural change. Cycling in high voltage range results in high capacity (∼132 mAh/g at 2.5 V), 99.7% Coulombic efficiency, superior rate performance (133 mAh/g at 3000 mA/g) and excellent stability (no fading at fast rate during more than 500 cycles). Cation vacancies in hollow iron oxide nanoparticles are also found to be responsible for the enhanced capacity in the conversion reactions. We monitored in situ structural transformation of hollow iron oxide nanoparticles by synchrotron X-ray absorption and diffraction techniques that provided us clear understanding of the lithium intercalation processes during electrochemical cycling.
In this study, we sought to find novel bacterial and metabolic hallmarks for bacterial vaginosis (BV). We studied the vaginal microbiome and metabolome of vaginal fluids from BV-affected patients (
n
... = 43) and healthy controls (
n
= 37) by means of an integrated approach based on quantitative polymerase chain reaction (qPCR) and proton nuclear magnetic resonance (
1
H-NMR). The correlations between the clinical condition and vaginal bacterial communities were investigated by principal component analysis (PCA). To define the metabolomics signatures of BV, 100 discriminant analysis by projection on latent structure (PLS-DA) models were calculated. Bacterial signatures distinguishing the health condition and BV were identified by qPCR.
Lactobacillus crispatus
strongly featured the healthy vagina, while increased concentrations of
Prevotella
,
Atopobium
and
Mycoplasma hominis
specifically marked the infection.
1
H-NMR analysis has led to the identification and quantification of 17 previously unreported molecules. BV was associated with changes in the concentration of metabolites belonging to the families of amines, organic acids, short chain fatty acids, amino acids, nitrogenous bases and monosaccharides. In particular, maltose, kynurenine and NAD
+
primarily characterised the healthy status, while nicotinate, malonate and acetate were the best metabolic hallmarks of BV. This study helps to better understand the role of the vaginal microbiota and metabolome in the development of BV infection. We propose a molecular approach for the diagnosis of BV based on quantitative detection in the vaginal fluids of
Atopobium
,
Prevotella
and
M. hominis
, and nicotinate, malonate and acetate by combining qPCR and
1
H-NMR.
To be able to control the functions of engineered multicomponent nanomaterials, a detailed understanding of heterogeneous nucleation at the nanoscale is essential. Here, by using in situ synchrotron ...X-ray scattering, we show that in the heterogeneous nucleation and growth of Au on Pt or Pt-alloy seeds the heteroepitaxial growth of the Au shell exerts high stress (∼2 GPa) on the seed by forming a core/shell structure in the early stage of the reaction. The development of lattice strain and subsequent strain relaxation, which we show using atomic-resolution transmission electron microscopy to occur through the slip of {111} layers, induces morphological changes from a core/shell to a dumbbell structure, and governs the nucleation and growth kinetics. We also propose a thermodynamic model for the nucleation and growth of dumbbell metallic heteronanostructures.
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