Small Cations Research Articles

Fretting damage behaviors of silicon nitride balls with different sintering aids and processes under grease lubrication

Taking silicon nitride (Si3N4) balls prepared using different sintering processes and sintering additives as objects, their tribological properties against bearing steel were investigated under grease lubrication conditions with heavy loads and high-frequency fretting, followed by analyzing the wear and fatigue damage behaviors. The results show that the Si3N4 balls prepared by adding 5AlEr and using the GPS1850 presented enhanced wear resistance and a low, stable friction coefficient ((6.10 ± 1.06)× 10−4 mm2). An appropriate increase in the temperature during GPS and selection of a sintering additive with a small cation radius were conducive to improving the wear resistance of Si3N4 balls. In addition, a strong adhesive friction film was formed through chemical reactions on the wear surface, which further protected the Si3N4 balls.

Heat capacity of molten alkali halides

Experimental data on the heat capacities of molten alkali halides near their melting points are analyzed depending on cation–anion composition. The isochoric heat capacities of all 20 liquid alkali halides were calculated using thermodynamic perturbation theory (TPT) based on a reference system of charged hard spheres + charge-induced dipole contribution to pairwise ionic interaction. Changes in the heat capacity depending on the ratio of ionic radii and polarizabilities are identified and described. On this basis, recommended heat capacity values are selected from the various experimental data. It is shown that the reduced isochoric heat capacity (CV/kB) should increase with a mismatch in the cation and anion radii as an even function with a minimum. Charge-induced dipole interactions lead to a breaking of the specific Coulomb symmetry, resulting in a more significant increase in the heat capacity for salts containing the smallest cations, as well as the anions with largest size and polarizability.

Effect of different alkali metal cations on the oxygen evolution activity and battery capacity of nickel electrodes in concentrated hydroxide electrolytes

The effect of different alkali metal cations on the oxygen evolution activity and battery capacity of nickel electrodes has recently been studied in low concentration alkali hydroxide electrolytes. As high concentration hydroxide electrolytes are favored in applications due to their high conductivity, we investigate if the cation effects observed in low concentration electrolytes translate to more industrially relevant conditions for both alkaline water electrolysis and nickel iron batteries. We investigate the alkali metal cation effect on the electrochemical properties of nickel electrodes in highly concentrated hydroxide electrolytes by adding Li+, Na+, Cs+ and Rb+ cations to a 6.5 M KOH electrolyte, while keeping the hydroxide concentration constant. For OER we find a trend in activity similar to that at low concentrations Rb+>Cs+>K+>Na+>Li+, where especially larger additions of Rb+ and Cs+ (1 M or 0.5 M) cause a significant decrease in OER potential. Smaller cations interact with the layered hydroxide structures in NiOOH to stabilize the α/γ phases and increase the potential for OER. The intercalation of small cations also causes an increase in battery electrode capacity because of the higher average valence of the Ni(OH)2/NiOOH α/γ pair. Small concentrations of Li+ added to a concentrated KOH electrolyte can therefore be beneficial for the nickel electrode battery functionality and for an integrated battery and electrolyser system, where it increases the battery capacity without a significant increase in OER onset potential.

Sub-Band Filling, Mott-like Transitions, and Ion Size Effects in C60 Single Crystal Electric Double Layer Transistors.

Electric double layer transistors (EDLTs) based on C60 single crystals and ionic liquid gates display pronounced peaks in sheet conductance versus gate-induced charge. Sheet conductance is maximized at electron densities near 0.5 e/C60 and is suppressed near 1 e/C60. The conductance suppression depends markedly on the choice of ionic liquid cation, with small cations favoring activated transport and essentially a complete shutdown of conductance at ∼1 e/C60 and larger cations favoring band-like transport, higher overall conductances at all charge densities up to 1.7 e/C60, and weaker suppression at 1 e/C60. Displacement current measurements on C60 EDLTs with small cations show clear evidence of sub-band filling at 1 e/C60, which correlates very well with the minimum in the C60 sheet conductance. Overall, the data suggest a significant Mott-Hubbard-like energy gap opens up in the surface density of states for C60 crystals gated with small cations. The causes of this energy gap may include both electron-electron repulsion and electron-cation attraction at the crystal/ionic liquid interface. The energy gap suppresses the insulator-to-metal transition in C60 EDLTs, but it can be manipulated by choice of electrolyte.

Classification of X-Ray Flare-driven Chemical Variability in Protoplanetary Disks

Abstract Young stars are highly variable in the X-ray regime. In particular, bright X-ray flares can substantially enhance ionization in the surrounding protoplanetary disk. Since disk chemical evolution is impacted by ionization, X-ray flares have the potential to fundamentally alter the chemistry of planet-forming regions. We present two-dimensional disk chemical models that incorporate a stochastic X-ray flaring module, named XGEN, and examine the flares’ overall chemical impact compared to models that assume a constant X-ray flux. We examine the impact of 500 yr of flaring events and find global chemical changes on both short timescales (days) in response to discrete flaring events and long timescales (centuries) in response to the cumulative impact of many flares. Individual X-ray flares most strongly affect small gas-phase cations, where a single flare can temporarily enhance the abundance of species such as H 3 + , HCO+, CH3 +, and C+. We find that flares can also drive chemistry out of “steady state” over longer time periods, where the disk-integrated abundance of some species, such as O and O2, changes by a few percent over the 500 yr model. We also explore whether the specific history of X-ray flaring events (randomly drawn but from the same energy distribution) impacts the chemical evolution and find that it does not. Finally, we examine the impact of X-ray flares on the electron fraction. While most molecules modeled are not highly sensitive to flares, certain species, including observable molecules, are very reactive to the dynamic environment of a young star.

Ultrastable and High Energy Calcium Rechargeable Batteries Enabled by Calcium Intercalation in a NASICON Cathode.

Ca-ion batteries (CIBs) have been considered a promising candidate for the next-generation energy storage technology owing to the abundant calcium element and the low reduction potential of Ca2+ /Ca. However, the large size and divalent nature of Ca2+ induce significant volume change and sluggish ion mobility in intercalation cathodes, leading to poor reversibly and low energy/power densities for CIBs. Herein, a polyanionic Na superionic conduction (NASICON)-typed Na-vacant Na1 V2 (PO4 )2 F3 (N1 PVF3 ) with sufficient interstitial spaces is reported as ultra-stable and high-energy Ca ion cathodes. The N1 PVF3 delivers exceptionally high Ca storage capacities of 110 and 65mAh g-1 at 10 and 500mA g-1 , respectively, and a record-long cyclability of 2000 cycles. More interestingly, by tailoring the fluorine content in N1 PVFx (1≤x≤3), the high working potential of 3.5V versus Ca2+ /Ca is achievable. In conjunction with Ca metal anode and a compatible electrolyte, Ca metal batteries with N1 VPF3 cathodes are constructed, which deliver an initial energy density of 342W h kg-1 , representing one of the highest values thus far reported for CIBs. Origins of the uncommonly stable and high-power capabilities for N1 PVF3 are elucidated as the small volume changes and low cation diffusion barriers among the cathodes.

The study of gramicidin a in both diblock and triblock PMOXA-PDMC copolymers using EPR spectroscopy

Gramicidin A is a hydrophobic peptide antibiotic produced by Bacillus brevis. This membrane protein, consisting of alternating L- and D- amino acids, forms an ion channel that is selective for small univalent cations. The orientation of this peptide and its head-to-head dimer formation are of special interest. This can be studied via synthetic polymer membranes and EPR spectroscopy. Diblock and triblock copolymers are used as mimetic systems in place of lipid bilayers. CW-EPR spectroscopy coupled with site directed spin labeling (SDSL) can provide important structural information that is traditionally difficult to obtain in systems such as biological membranes.

Experimentally probing ionic solutions in single-digit nanoconfinement

Understanding ionic solutions in single-digit nanoconfinement is crucial to explain the behavioral transition of confined solutions. This is particularly the case when the system length scale crosses the classical key length scales describing energetics and equilibrium of ionic solutions next to surfaces. Experimentally probing nanoconfinement would open large perspectives to test modelling or theory predictions. Here, using a new test vehicle that consists in 3 and 5 nm-height silica nanochannels associated with an original characterization technique based on the interface hard X-ray reflectivity analysis, we directly probed the transport of solutions containing cations having increasing kosmotropic properties (XCl2 with X: Ba < Ca < Mg) and obtained their distributions inside the nanochannels. We observed that cation adsorption decreases with the size of the confinement and that small cation adsorption is favored. In addition, nanochannel clogging occurs when ions tend to form ion pairs. These ion pairs may play the role of nano-sized prenucleation clusters leading to phase precipitation. These results evidence the specific ion effect in single-digit nanoconfinement that may result in dramatic changes of solution properties. In this line, our new method opens new perspectives for the characterization of ionic solutions and of interfaces in single-digit nanoconfinement.

Five new isomorphic coordination polymers with large conjugated ligands: Synthesis, crystal structures and performances

Five new coordination compounds with isomorphic frameworks, {[M(cpp)2(H2O)2]·3H2O}n [M ​= ​Co (1), Cd (2), Mn (3), Ni (4), Zn (5)], were successfully synthesized through the reactions of 1-(4-carboxyphenyl)-3-(pyrazin-2-yl)pyrazole (Hcpp) and a series of transition metal salts under the solvo-thermal conditions. Compounds 1–5 were characterized by single crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, infrared spectra and thermogravimetric analysis. Isomorphic compounds 1–5 display an abnormal two-dimensional helical layer containing a M4(cpp)4 cavity with the dimension of 26.21 ​× ​8.39 ​Å2. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic interactions with Curie constant (2.08 ​cm3 ​K ​mol−1) and Weiss constant (−6.90 ​K) in compound 1. Compounds 2 and 5 show apparently blue light emission, wherein the sensing responses to small molecules, inorganic anions and metal cations indicate compound 5 can be used as a multifunctional fluorescence probe to detect aniline, Fe3+, CrO42− and Cr2O72− through fluorescence quenching and the corresponding quenching mechanisms are proposed.

Effect of Y2O3 content on the microstructural characteristics and the mechanical and thermal properties of Yb-doped SiAlON ceramics

SiAlON ceramics are primarily employed in ceramic cutting tools, which exploit their stable physical properties in high-temperature cutting environments due to their excellent mechanical properties. Here, Yb/Y-co-doped SiAlON ceramics are prepared by adding Yb and Y rare-earth (RE) ions in the RExSi12-(m+n)Alm+nOnN16-n (m = 0.4, n = 1.0) composition. Yb2O3, the RE oxide, is the main sintering additive. For REx composition design with (Yb1-y + Yy)x, Yb2O3 is replaced by Y2O3 (y = 0.00, 0.25, 0.50, 0.75, 1.00). While Yb2O3 has excellent high-temperature stability, it is limited by its microstructural characteristics, that is, the β-SiAlON morphology and limited fracture toughness due to the small cation sizes. Thus, the changes in the above properties are investigated for various Y2O3 additive contents substituting for Yb2O3. The average grain width decreases, and the equiaxed β-SiAlON grains are elongated with increasing Y2O3 content. Regarding the mechanical properties, the hardness and fracture toughness are evaluated using the indentation fracture method. The hardness decreases with increasing Y2O3 content; however, the fracture toughness exhibits a significant increase (∼53.6%) from 4.6 to 7.0 MPa⋅m1/2. Regarding crack propagation, intergranular fracture is mainly observed in the Yb/Y-co-doped SiAlON ceramics, whereas transgranular fracture is primarily observed in the Yb-single-doped SiAlON ceramic. Y2O3 substitution increases the α/β-SiAlON phase ratio, and the grain boundary phase exhibits increasing vitrification with increasing Y2O3 content. Moreover, the thermal properties of the Yb/Y-co-doped compositions are analyzed and discussed regarding intrinsic properties such as phonon scattering. The microstructural characteristics and improved fracture toughness derived from the Yb/Y-co-doped system designed in this study suggest considerable potential for the future composition design of ceramic cutting tools.

Molecular basis of Arginine and Lysine DNA sequence-dependent thermo-stability modulation.

We have used a variety of theoretical and experimental techniques to study the role of four basic amino acids–Arginine, Lysine, Ornithine and L-2,4-Diaminobutyric acid–on the structure, flexibility and sequence-dependent stability of DNA. We found that the presence of organic ions stabilizes the duplexes and significantly reduces the difference in stability between AT- and GC-rich duplexes with respect to the control conditions. This suggests that these amino acids, ingredients of the primordial soup during abiogenesis, could have helped to equalize the stability of AT- and GC-rich DNA oligomers, facilitating a general non-catalysed self-replication of DNA. Experiments and simulations demonstrate that organic ions have an effect that goes beyond the general electrostatic screening, involving specific interactions along the grooves of the double helix. We conclude that organic ions, largely ignored in the DNA world, should be reconsidered as crucial structural elements far from mimics of small inorganic cations.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids.

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host–guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Thermal, structural and dynamic properties of ionic liquids and organic ionic plastic crystals with a small ether-functionalised cation

A series of new salts with a small ether-functionalised trimethylammonium cation are synthesised and characterised to probe their unique structure–property relationships.

Aziridinium cation templating 3D lead halide hybrid perovskites.

This study describes the synthesis of the first aziridinium-based compounds, namely hybrid perovskites (AzrH)PbHal3 (where AzrH = aziridinium, Hal = Cl, Br or I). This highly reactive species was stabilized in 3D lead halide frameworks and was found to be a small enough organic cation to promote the formation of semiconducting organo-inorganic materials.

Predicting the photon energy of quasi-2D lead halide perovskites from the precursor composition through machine learning.

Quasi-2D perovskites with the general formula of L2An−1PbnX3n+1 (L = organic spacer cation, A = small organic cation or inorganic cation, X = halide ion, and n ≤ 5) are an emerging kind of luminescent material. Their emission color can be easily tuned by their composition and n value. Accurate prediction of the photon energy before experiments is essential but unpractical based on present studies. Herein, we use machine learning (ML) to explore the quantitative relationship between the photon energies of quasi-2D perovskite materials and their precursor compositions. The random forest (RF) model presents high accuracy in prediction with a root mean square error (RMSE) of ∼0.05 eV on a test set. By feature importance analysis, the composition of the A-site cation is found to be a critical factor affecting the photon energy. Moreover, it is also found that the phase impurity greatly lowers the photon energy and needs to be minimized. Furthermore, the RF model predicts the compositions of quasi-2D perovskites with high photon energies for blue emission. These results highlight the advantage of machine learning in predicting the properties of quasi-2D perovskites before experiments and also providing color tuning directions for experiments.

Enhancing the Luminance Efficiency of Formamidinium-Based Dion-Jacobson Perovskite Light-Emitting Diodes via Compositional Engineering.

In this paper, the phase formation mechanism of formamidinium (FA)-based Dion-Jacobson (DJ) perovskites is uncovered for the first time, which includes the formation of the n1 domain (n = 1 perovskite phase) and a trace amount of the large n domain in the spin-coating process and the growth of the n2 domain and the large n domain during the thermal annealing stage. The phase formation mechanism clearly reveals the different phase distributions between FA-based Ruddlesden-Popper (RP) and FA-based DJ perovskite films at different stages of film preparation due to the larger formation energy of the DJ perovskites. According to this phase formation mechanism, we put forward an effective strategy of the small A-site cation compositional engineering. Then, excess perovskitizer cations (FA+) are introduced to increase the crystallinity, modulate the phase distribution and passivate defects without disturbing the structure of DJ perovskites simultaneously. The final green-light DJ PeLED devices show a maximum luminance of 41 520 cd/m2 and a maximum current efficiency of 31.1 cd/A (EQE: 8.5%), which are the record values so far. The final DJ PeLEDs show an improved operational lifetime of ca. 15 min at an initial luminance of ca. 800 cd/m2. Our results suggest that DJ perovskites can be promising for light-emitting applications.

Tracing electron density changes in langbeinite under pressure.

Pressure is well known to dramatically alter physical properties and chemical behaviour of materials, much of which is due to the changes in chemical bonding that accompany compression. Though it is relatively easy to comprehend this correlation in the discontinuous compression regime, where phase transformations take place, understanding of the more subtle continuous compression effects is a far greater challenge, requiring insight into the finest details of electron density redistribution. In this study, a detailed examination of quantitative electron density redistribution in the mineral langbeinite was conducted at high pressure. Langbeinite is a potassium magnesium sulfate mineral with the chemical formula [K2Mg2(SO4)3], and crystallizes in the isometric tetartoidal (cubic) system. The mineral is an ore of potassium, occurs in marine evaporite deposits in association with carnallite, halite and sylvite, and gives its name to the langbeinites, a family of substances with the same cubic structure, a tetrahedral anion, and large and small cations. Single-crystal X-ray diffraction data for langbeinite have been collected at ambient pressure and at 1 GPa using a combination of in-house and synchrotron techniques. Experiments were complemented by theoretical calculations within the pressure range up to 40 GPa. On the basis of changes in structural and thermal parameters, all ions in the langbeinite structure can be grouped into 'soft' (potassium cations and oxygens) and 'hard' (sulfur and magnesium). This analysis emphasizes the importance of atomic basins as a convenient tool to analyse the redistribution of electron density under external stimuli such as pressure or temperature. Gradual reduction of completeness of experimental data accompanying compression did not significantly reduce the quality of structural, electronic and thermal parameters obtained in experimental quantitative charge density analysis.

Structural evidence of mixed alkali effect for aluminoborosilicate glasses

The structure of mixed alkali aluminoborosilicate is quite difficult to explain due to the mixed alkali effect and interaction between multiple network formers, intermediate oxides, and network modifiers. To understand the complex behavior of these components in mixed alkali glasses, solid-state MAS NMR and Raman spectroscopy were performed. Various Raman peaks were specifically revealed, and all of which were highly associated with the degree of polymerization (DP) obtained by deconvolution of 800–1200 cm−1. A systematic change of the glass network was well explained to be a consequence of a strong relationship between DP and MAS NMR results of network formers (27Al and 11B). When alkali cations were mixed, a new characteristic of mixed alkali effect, an increase in charge compensation stability between AlO4 and smaller cation, was first observed from high correlation between full width at half maximum (FWHM) of network modifiers (7Li and 23Na) and MAS NMR data of network formers.

Characterization of Structure and Dynamics of the Guanidine-II Riboswitch from Escherichia coli by NMR Spectroscopy and Small-Angle X-ray Scattering (SAXS).

Riboswitches are regulatory RNA elements that undergo functionally important allosteric conformational switching upon binding of specific ligands. The here investigated guanidine‐II riboswitch binds the small cation, guanidinium, and forms a kissing loop‐loop interaction between its P1 and P2 hairpins. We investigated the structural changes to support previous studies regarding the binding mechanism. Using NMR spectroscopy, we confirmed the structure as observed in crystal structures and we characterized the kissing loop interaction upon addition of Mg2+ and ligand for the riboswitch aptamer from Escherichia coli. We further investigated closely related mutant constructs providing further insight into functional differences between the two (different) hairpins P1 and P2. Formation of intermolecular interactions were probed by small‐angle X‐ray scattering (SAXS) and NMR DOSY data. All data are consistent and show the formation of oligomeric states of the riboswitch induced by Mg2+ and ligand binding.

Alkaline Stability Evaluation of Polymerizable Hexyl-Tethered Ammonium Cations.

One of the important challenges in designing robust alkaline anion exchange membranes is the difficulty associated with the chemical stability of covalently bound cationic units. Here, a systematic study exploring alkaline stabilities of polymerizable hexyltrimethylammonium cations is presented, where the hexyl chain is linked to a phenyl ring through a direct carbon-carbon, phenyl ether, or benzyl ether functionality. For this work, small molecule model compounds, styrenic monomer analogs, and their homopolymers are synthesized. Alkaline stabilities of the small molecule cations and their homopolymers are compared to alkaline stability of benzyltrimethylammonium (BTMA) cation and its homopolymer poly(BTMA), respectively. All the hexyl-tethered cations and their homopolymers are significantly more stable under strongly alkaline conditions (2 m KOD at 80 °C). Moreover, ether-linked cations show comparable stability to the direct carbon-carbon linked cation. Via 1 H NMR analyses, possible degradation mechanisms are investigated for each small molecule cation. Findings of this study strongly suggest that the alkaline stability is dictated by the steric hindrance around the β-hydrogen. This study expands beyond the limits of general knowledge on alkaline stability of alkyl-tethered ammonium cations via the Hofmann elimination route, highlights important design parameters for stable ammonium cations, and demonstrates accessible directly polymerizable alkaline stable ammonium cations.