Larger Alkali Ions Research Articles

Defect Engineering of Nanocrystal‐In‐Glass Composites for Ultrashort Optical Pulse Monitoring

AbstractThe rational control of intrinsic defects in materials can significantly enhance their scientific and technological potentials, but it remains a long‐standing challenge in nanocrystal‐in‐glass composites (NGCs). Herein, a defect engineering strategy mediated by the mixed alkali effect is proposed and experimentally demonstrated for NGCs. Interestingly, the hybridization of large alkali ions can effectively increase the barrier of Li+ migration and reduce the Li‐related defects in LiNbO3 NGC. As a result, a novel LiNbO3 NGC with greatly reduced Li‐related defects, high crystallinity of over 60%, and excellent optical transmission are successfully fabricated. This unique NGC configuration facilitates efficient transverse second harmonic generation (TSHG) in a broad wavelength region. Based on the above effects, a standard TSHG device is fabricated and implemented to monitor ultrashort optical pulses with duration in the order of ≈10−13 s over a broad wavelength region, down to 780 nm. The proposed strategy not only provides a new idea for defect engineering in materials science but also has great significance for boosting the practical applications of NGCs in ultrashort optical pulse monitoring.

Stabilization of Guest Molecules inside Cation-Lidded Cucurbiturils Reveals that Hydration of Receptor Sites Can Impede Binding.

Docking of alkali metal ions to water-soluble macrocyclic receptors generally reduces the affinity of guest molecules due to competitive binding. The idea that solvation water molecules could display a larger steric hindrance towards guest binding than cations has not been considered to date. We show that the docking of large cations to cucurbit[5]uril (CB5) unexpectedly increases (by a factor of 5-8) the binding of hydrophobic guests, methane and ethane. This is due to the removal of water molecules from the carbonyl portals of CB5 during cation binding, which frees up space for hydrophobe encapsulation. In contrast, smaller cations like sodium protrude deeply into the cavity of CB5 and cause the expected decrease in binding, such that the rational selection of alkali cations allows for a variation of up to a factor of 20 in binding of methane and ethane. The statistical analysis of crystallographic data shows that the cavity volume of CB5 can be enlarged by placing large alkali ions (Rb+ and Cs+ ) centro-symmetrically at the portals. The results reveal a hitherto elusive steric hindrance of solvation water molecules near receptor binding sites, which is pertinent for the design of supramolecular catalysts and the understanding of biological receptors.

Stabilization of Guest Molecules inside Cation‐Lidded Cucurbiturils Reveals that Hydration of Receptor Sites Can Impede Binding

AbstractDocking of alkali metal ions to water‐soluble macrocyclic receptors generally reduces the affinity of guest molecules due to competitive binding. The idea that solvation water molecules could display a larger steric hindrance towards guest binding than cations has not been considered to date. We show that the docking of large cations to cucurbit[5]uril (CB5) unexpectedly increases (by a factor of 5–8) the binding of hydrophobic guests, methane and ethane. This is due to the removal of water molecules from the carbonyl portals of CB5 during cation binding, which frees up space for hydrophobe encapsulation. In contrast, smaller cations like sodium protrude deeply into the cavity of CB5 and cause the expected decrease in binding, such that the rational selection of alkali cations allows for a variation of up to a factor of 20 in binding of methane and ethane. The statistical analysis of crystallographic data shows that the cavity volume of CB5 can be enlarged by placing large alkali ions (Rb+ and Cs+) centro‐symmetrically at the portals. The results reveal a hitherto elusive steric hindrance of solvation water molecules near receptor binding sites, which is pertinent for the design of supramolecular catalysts and the understanding of biological receptors.

Hydrogen defects in feldspars: alkali-supported dehydrogenation of sanidine

In the first two papers of this series [Behrens, Phys Chem Minerals 48:8, 2021a; Behrens, Phys Chem Minerals 48:27, 2021b], incorporation of hydrogen in the feldspar structure, partitioning of hydrogen between feldspars and gases/fluids and self-diffusion of hydrogen in feldspars have been discussed, with particular focus on sanidine. Here, the results of reactions between sanidine containing strongly bonded hydrogen defects and (Na,K)Cl are presented. Experiments were performed at ambient pressure at temperatures of 605–1000 °C, and hydrogen profiles were measured by IR microspectroscopy. Profiles can be interpreted by an incomplete dehydrogenation at the crystal surface or a strong concentration dependence of hydrogen diffusivity. Both are consistent with hydrogen located on interstitial sites and difficult to substitute by the larger alkali ions. Chemical diffusivities of hydrogen derived from fitting of the profiles or Boltzmann–Matano analysis are similar to self-diffusivities determined by D/H exchange experiments. Activation energies are also comparable. Comparison to sodium and potassium diffusion data for sanidine (Wilangowski et al. in Defect Diffus Forum 363: 79–84, 2015; Hergemöller et al. in Phys Chem Minerals 44:345–351, 2017) supports a mechanism of proton diffusion charge-compensated by Na+ diffusion for hydrogen removal in the sanidines under dry conditions.

(Invited) From Layered Oxides to Disordered Rocksalt Cathodes: The Role of Electronic Structure, Cation Order, and Structure on the Performance of Dense Cathode Materials

Layered cathode materials are the enabler of today’s Li-ion industry. I will review some of the fundamental relations between electronic structure, cation ordering, and electrochemical performance in layered Li, Na and K-compounds. Diffusion in layered cathodes occurs through a divacancy mechanism which enables the low-energy Li passage through the tetrahedral sites that connect the octahedral positions in the Li layers. This diffusion mechanism provides high rate capability to layered cathodes, but relies on the Li-slab spacing to remain large upon electrochemical cycling. Any migration of transition metals into the Li-layer tends to contract the slab spacing and reduce rate capability. This limits practical layered materials to the NMC chemistry as Ni, Co and Mn4+ are the only ions that have a strong enough octahedral ligand-field stabilization to remain in the transition metal layer upon cycling. This problem is less pronounced for Na-layered oxides as the larger slab spacing makes occupancy of the tetrahedral and octahedral site in the Na-layer much less favorable for transition metals. But layered oxides with large alkali ions such as Na+ and K+ suffer from more sloped voltage profiles with limits their usable energy density.Finally, I will show how the chemical diversity of Li-ion cathodes can be extended to a much broader set of elements by enabling Li-excess disordered rocksalts (DRX). These materials diffuse lithium ions through a statistical network of low-energy migration environments, and have recently been shown to have very high capacity and rate performance.

Coupling of diffusion and chemical stress: The case of ion exchange in glass

AbstractThe chemical strengthening of glass results from an ion exchange process in which smaller alkali ions in a glass are replaced with larger alkali ions from a molten salt bath. This interdiffusion process leads to a buildup of chemical stress in the glass. However, traditional modeling of the ion exchange process has not fully accounted for interaction effects between mass diffusion and the chemical stress developed during the process. In this study, we develop the general theory of coupling between diffusion and stress, resulting in a single flux equation with a concentration‐ and stress‐dependent interdiffusion coefficient. We apply the theory to the specific cases of chemically strengthened soda lime silicate and aluminosilicate glasses, demonstrating the impact of interaction terms on concentration profiles and interdiffusion coefficient. Following a phenomenological approach, this study demonstrates the effect of the interdiffusion on stress generation and vice versa to account for deviations from the simple expressions published hitherto in the literature.

The Electrical Conductivity of Liebermannite: Implications for Water Transport Into the Earth's Lower Mantle

AbstractLiebermannite (KAlSi3O8) is a principal mineral phase expected to be thermodynamically stable in deeply subducted continental and oceanic crusts. The crystal structure of liebermannite exhibits tunnels that are formed between the assemblies of double chains of edge‐sharing (Si, Al) O6 octahedral units, which act as a repository for large incompatible alkali ions. In this study, we investigate the electrical conductivity of liebermannite at 12, 15, and 24 GPa and temperature of 1500 K to track subduction pathways of continental sediments into the Earth's lower mantle. Further, we looked at whether liebermannite could sequester incompatible H2O at deep mantle conditions. We observe that the superionic conductivity of liebermannite due to the thermally activated hopping of K+ ions results in high electrical conductivity of more than 1 S/m. Infrared spectral features of hydrous liebermannite indicate the presence of both molecular H2O and hydroxyl (OH−) groups in its crystal structure. The observed high electrical conductivity in the mantle transition zone beneath Northeastern China and the lower mantle beneath the Philippine Sea can be attributed to the subduction pathways of continental sediments deep into the Earth's mantle. While major mineral phases in pyrolitic compositions are almost devoid of H2O under lower mantle conditions, our study demonstrates that liebermannite could be an important host of H2O in these conditions. We propose that the relatively high H2O contents of ocean island basalts derived from deep mantle plumes are primarily related to deeply subducted continental sediments, in which liebermannite is the principal H2O carrier.

Size-, Water-, and Defect-Regulated Potassium Manganese Hexacyanoferrate with Superior Cycling Stability and Rate Capability for Low-Cost Sodium-Ion Batteries.

Potassium manganese hexacyanoferrate (KMHCF) is a low-cost Prussian blue analogue (PBA) having a rigid and open framework that can accommodate large alkali ions. Herein, the synthesis of KMHCF and its application as a high-performance cathode in sodium-ion batteries (NIBs) is reported. High-quality KMHCF with low amounts of crystal water and defects and with homogeneous microstructure is obtained by controlling the nucleation and grain growth by using a high-concentration citrate solution as a precipitation medium. The obtained KMHCF exhibits superior cycling and rate performance as a NIB cathode, showing 80% capacity retention after 1000 cycles at 1 C and a high capacity of 95 mA h g-1 at 20 C. Unlike conventional single-cation batteries, the hybrid NIB with KMHCF as cathode and Na as anode in Na-ion electrolyte displays three reversible plateaus that involve stepwise insertion/extraction of both K+ and Na+ in the PBA framework. In later cycling, the K+ -Na+ cointercalated phase is partially converted into a cubic sodium manganese hexacyanoferrate (NaMHCF) phase due to the increasing replacement of Na+ for K+ .

Reversible Insertion in AFeF3 (A = K+, NH4+) Cubic Iron Fluoride Perovskites.

The search for new cathode materials is primordial for alkali-ion battery systems, which are facing a constantly growing demand for high energy density storage devices. In quest of more performing active compounds on the positive side, anhydrous iron(III) fluoride demonstrated to be a good compromise in terms of high capacity, operating voltage, and low cost. However, its reaction toward lithium leads to complicated insertion/conversion reactions, which hinder its performances in Li-ion cells. Cycling this material against larger ions such as sodium and potassium is hard or simply impossible due to the size of the channels of the FeF3 framework impeding ions diffusion. Herein, we propose a strategy based on the use of cubic perovskite AFeF3 (A = K+, NH4+) as starting materials, allowing the straightforward insertion (after a first disinsertion of the alkali and/or NH4+ ion) of lithium within the structure and enabling the cycling toward larger alkali ions such as sodium and potassium. For example, a cubic KFeF3 perovskite, produced by a facile synthesis method, shows superior rate capability toward lithium retaining a capacity of up to 132 mA·h·g-1 at 5 C or of 120 mA·h·g-1 at 5 C toward sodium and enabling cycling toward potassium. Moreover, cubic NH4FeF3 perovskite is discussed for the first time as the suitable cathode material for alkali-ion batteries.

Investigating PID Shunting in Polycrystalline CIGS Devices via Multi-Scale, Multi-Technique Characterization

We investigated potential-induced degradation (PID) in CuIn1-xGaxSe2 (CIGS) mini-modules stressed in the laboratory. Small cores were removed from the modules and were subjected to analysis. We completed a proof-of-concept correlative study relating cathodoluminescence to sodium content via time-of-flight secondary-ion mass spectrometry imaging. By comparing one-dimensional depth profile results and three-dimensional tomography results on stressed and unstressed CIGS mini-modules, we can see that PID in CIGS results from sodium migration through absorber, most likely via grain boundaries. Potassium concentration distributions show little change when adding a voltage bias to a temperature and humidity stress. This suggests doping with other large alkali ions, such as cesium and rubidium, rather than sodium can increase the PID resistance of CIGS modules.

Increasing stripe-type fluctuations in AFe2As2 ( A=K , Rb, Cs) superconductors probed by As75 NMR spectroscopy

We report $^{75}$As nuclear magnetic resonance measurements on single crystals of RbFe$_{2}$As$_{2}$ and CsFe$_{2}$As$_{2}$. Taking previously reported results for KFe$_{2}$As$_{2}$ into account, we find that the anisotropic electronic correlations evolve towards a magnetic instability in the $A$Fe$_{2}$As$_{2}$ series (with $A$ = K, Rb, Cs). Upon isovalent substitution with larger alkali ions, a drastic enhancement of the anisotropic nuclear spin-lattice relaxation rate and decreasing Knight shift reveal the formation of pronounced spin fluctuations with stripe-type modulation. Furthermore, a decreasing power-law exponent of the nuclear spin-lattice relaxation rate $(1/T_{1})_{H\parallel{ab}}$, probing the in-plane spin fluctuations, evidences an emergent deviation from Fermi-liquid behavior. All these findings clearly indicate that the expansion of the lattice in the $A$Fe$_{2}$As$_{2}$ series tunes the electronic correlations towards a quantum critical point at the transition to a yet unobserved, ordered phase.

Chemical Strengthening of Alkali‐Free Glass via Pressure Vessel Ion Exchange

Ion exchange is a popular technique for chemically strengthening alkali‐containing glass articles, such as Corning® Gorilla® Glass. The ion exchange process is based on a replacement of small alkali ions in the glass with larger alkali ions from a molten salt bath through inter‐diffusion. As the larger alkali ions from the salt bath supplant the smaller alkali ions in the glass, a compressive stress profile is generated near the surface of the glass, which increases its strength and damage resistance. However, certain applications of high‐tech glasses require alkali‐free environments, such as glasses used as substrates for flat panel display applications. In this paper, we report the first successful chemical strengthening of an alkali‐free glass. This is achieved via an aqueous ion exchange of barium salts under high pressure and temperature. X‐ray photoelectron spectroscopy reveals that Ba2+ replaces both Ca2+ and B3+ in the glass, producing surface compressive stress values near 200 MPa. This technology may enable chemical strengthening for a wide range of applications, including flat panel display substrates.

An economic route to mass production of graphene oxide solution for preparing graphene oxide papers

Abstract Graphene oxide paper (GOP) is a composite material fabricated from graphene oxide (GO) solution. In addition, it can be a novel and potential material for application on the separation of water vapor from gaseous steam or larger alkali ions from aqueous solution. GOP could be used as electricity and thermal storage materials. The preparation of GO commonly uses high purity natural or artificial graphite. It is difficult to prepare GOP from artificial graphite powder due to the cost of $1,450 US/ton. In this study, we tried to prepare GOPs from homemade graphene sheets containing carbon materials (GSCCMs) and evaluate the thermal properties of GSCCM derived GOPs. Results show that GSCCM derived GOPs have a higher phase transition temperature, and the average mesophase phase change enthalpy is 9.41 J/g, which is 2.87 times higher than graphite derived GOP. Therefore, to prepare GOP from GSCCMs could highly reduce the cost.

Non-conservation of the total alkali concentration in ion-exchanged glass

Chemically strengthened glasses are widely used in applications requiring high scratch and damage resistance, such as cover glass for personal electronic devices. Chemical strengthening occurs by replacing the smaller alkali ions in the glass by larger alkali ions from a molten salt bath, whereby a surface layer with high compressive stress is installed. The mechanical properties of chemically strengthened glass strongly depend on the magnitude of the compressive stress, which in turn is proportional to the concentration of exchanged alkali ions. It has hitherto been assumed that the total amount of alkali ions in the glass is conserved during the ion exchange (e.g., in the Nernst–Planck model). In this work, we immerse alkali aluminosilicate glasses [30M2O·10Al2O3·60SiO2 (mol%)] in MNO3 salt baths containing identical alkali ions (where M=Li, Na, K). We demonstrate a non-conservation of the total amount of alkali ions in the glass during the ion exchange process. Generally we find that the smaller ions exhibit a net flux into the glass, while the larger ions demonstrate a net flux into the salt bath. Moreover, the total amount of alkali ions in the top surface layer is not conserved in sodium and potassium aluminosilicate glasses after ion exchange. We explain these findings based on the thermodynamic driving force difference in alkali oxides residing in glass or nitrate salt. The results are important for chemical strengthening applications, since the direction of flux and the non-conservation of alkali ions affect the final compressive stress of an ion exchanged glass.

Ion-size effect at the surface of a silica hydrosol

Using synchrotron x-ray reflectivity, I studied the ion-size effect for alkali ions (Na(+), K(+), Rb(+), and Cs(+)), with densities as high as 4x10(18)-7x10(18) m(-2), suspended above the surface of a colloidal solution of silica nanoparticles in the field generated by the surface electric-double layer. I found that large alkali ions preferentially accumulate and replace smaller ones at the surface of the hydrosol, a result qualitatively agreeing with the dependence of the Kharkats-Ulstrup single-ion electrostatic free energy on the ion's radius.

Ion transport mechanism in borate glasses: Influence of network structure on non-Arrhenius conductivity

In this paper, we report a non-Arrhenius behavior in the temperature-dependent dc conductivity of alkali ion conducting borate glasses below their glass transition. This behavior is strongly influenced by the alkali oxide content and by the type of the alkali ions, and is most pronounced in glasses with low alkali oxide content and with large alkali ions. In contrast to many fast ion conducting glasses, the curvature in the Arrhenius plot is positive. Furthermore, we show that annealing of the glass samples leads to a partial recovery of the Arrhenius behavior. Our experimental results are interpreted in terms of local structural changes in the borate network with temperature, which have been detected by means of solid state NMR spectroscopy.

Ion Specificity and Ionic Strength Dependence of the Osmoregulatory ABC Transporter OpuA

The ATPase subunit of the osmoregulatory ATP-binding cassette transporter OpuA from Lactococcus lactis has a C-terminal extension, the tandem cystathionine beta-synthase (CBS) domain, which constitutes the sensor that allows the transporter to sense and respond to osmotic stress (Biemans-Oldehinkel, E., Mahmood, N. A. B. N., and Poolman, B. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 10624-10629). C-terminal of the tandem CBS domain is an 18-residue anionic tail (DIPDEDEVEEIEKEEENK). To investigate the ion specificity of the full transporter, we probed the activity of inside-out reconstituted wild-type OpuA and the anionic tail deletion mutant OpuADelta12; these molecules have the tandem CBS domains facing the external medium. At a mole fraction of 40% of anionic lipids in the membrane, the threshold ionic strength for activation of OpuA was approximately 0.15, irrespective of the electrolyte composition of the medium. At equivalent concentrations, bivalent cations (Mg(2+) and Ba(2+)) were more effective in activating OpuA than NH(4)(+), K(+), Na(+), or Li(+), consistent with an ionic strength-based sensing mechanism. Surprisingly, Rb(+) and Cs(+) were potent inhibitors of wild-type OpuA, and 0.1 mM RbCl was sufficient to completely inhibit the transporter even in the presence of 0.2 M KCl. Rb(+) and Cs(+) were no longer inhibitory in OpuADelta12, indicating that the anionic C-terminal tail participates in the formation of a binding site for large alkali metal ions. Compared with OpuADelta12, wild-type OpuA required substantially less potassium ions (the dominant ion under physiological conditions) for activation. Our data lend new support for the contention that the CBS module in OpuA constitutes the ionic strength sensor whose activity is modulated by the C-terminal anionic tail.

A new surface structural approach to ion adsorption: Tracing the location of electrolyte ions

Electrolyte ions differ in size leading to the possibility that the distance of closest approach to a charged surface differs for different ions. So far, ions bound as outersphere complexes have been treated as point charges present at one or two electrostatic plane(s). However, in a multicomponent system, each electrolyte ion may have its own distance of approach and corresponding electrostatic plane with an ion-specific capacitance. It is preferable to make the capacitance of the compact part of the double layer a general characteristic of the solid–solution interface. A new surface structural approach is presented that may account for variation in size of electrolyte ions. In this approach, the location of the charge of the outersphere surface complexes is described using the concept of charge distribution in which the ion charge is allowed to be distributed over two electrostatic planes. It was shown that the concept can successfully describe the pH dependent proton binding and the shift in the isoelectric point (IEP) in the presence of variety of monovalent electrolyte ions, including Li +, Na +, K +, Cs +, Cl −, NO − 3, and ClO − 4 with a common set of parameters. The new concept also sheds more light on the degree of hydration of the ions when present as outersphere complexes. Interpretation of the charge distribution values obtained shows that Cl − ions are located relatively close to the surface. The large alkali ions K +, Cs +, and Rb + are at the largest distance. Li +, Na +, NO − 3, and ClO − 4 are present at intermediate positions.

Mixed Alkali Effect as a Retarding Effect of Secondary Diffusion Processes in Glass

ABSTRACTIon mobility in mixed alkali glass is discussed in the context of the recent experimental observation that oxygen diffusion from molten salt into glass accompanies the replacement of smaller alkali ions for larger alkali ions during ion exchange. The assumption is made that simultaneous migration of two unlike monovalent cations induces, among other things, oxygenexchange diffusion between sites. Diffusing oxygen molecules form additional fluctuating sites or traps lying along the ion pathways between regular ionic sites. Instead of jumping directly to the regular ionic site, mobile ions are forced to execute several additional hops between fluctuating sites, and this results in significant reduction in ion mobility.

Superconductivity in Alkali-Ammonia Complex Fullerides

Abstract Here we show that low temperature synthesis in liquid ammonia successfully stablied the combination of one Na and two large alkali ions(K and Rb) by incorporating NH3 molecules. Both (NH3)xNaK2C60 and (NH3)xNaRb2C60 (x∼0.8) retained the fcc cell with a=14.37 A and a=14.52 A, and superconduct at 11K and 13K, respectively. A Na-NH3 cluster occupies the octahedral interstice and remaining K or Rb occupies the tetrahedral site. The Na ion is displaced by 0.4–0.6 A from the center of the octahedral site. The present system thus provides an example of fcc superconductors involving off-centered cations that exhibit different trend in the well known relationship between transition temperature (T c ) and lattice parameter of face-centered cubic A3C60 (A=alkali metals) superconductors.13