Pure Alkali Metal Research Articles

Construction and Structural Transformation of Metal-Organic Nanostructures Induced by Alkali Metals and Alkali Metal Salts.

Metal-organic nanostructures are attractive in a variety of scientific fields, such as biomedicine, energy harvesting, and catalysis. Alkali-based metal-organic nanostructures have been extensively fabricated on surfaces based on pure alkali metals and alkali metal salts. However, their differences in the construction of alkali-based metal-organic nanostructures have been less discussed, and the influence on structural diversity remains elusive. In this work, from the interplay of scanning tunneling microscopy imaging and density functional theory calculations, we constructed Na-based metal-organic nanostructures by applying Na and NaCl as sources of alkali metals and visualized the structural transformations in real space. Moreover, a reverse structural transformation was achieved by dosing iodine into the Na-based metal-organic nanostructures, revealing the connections and differences between NaCl and Na in the structural evolutions, which provided fundamental insights into the evolution of electrostatic ionic interactions and the precise fabrication of alkali-based metal-organic nanostructures.

Nonstoichiometric Salt Intercalation as a Means to Stabilize Alkali Doping of 2D Materials.

Although doping with alkali atoms is a powerful technique for introducing charge carriers into physical systems, the resulting charge-transfer systems are generally not air stable. Here we describe computationally a strategy towards increasing the stability of alkali-doped materials that employs stoichiometrically unbalanced salt crystals with excess cations (which could be deposited during, e.g., insitu gating) to achieve doping levels similar to those attained by pure alkali metal doping. The crystalline interior of the salt crystal acts as a template to stabilize the excess dopant atoms against oxidation and deintercalation, which otherwise would be highly favorable. We characterize this doping method for graphene, NbSe_{2}, and Bi_{2}Se_{3} and its effect on direct-to-indirect band gap transitions, 2D superconductivity, and thermoelectric performance. Salt intercalation should be generally applicable to systems which can accommodate this "ionic crystal" doping (and particularly favorable when geometrical packing constraints favor nonstoichiometry).

Stokes-Einstein Relation in Pure Alkali Metals and their Alloys

Stokes-Einstein relation is a convenient way to evaluate diffusion properties in liquids from viscosity results (and vice-versa). However, the accuracy of this relation in the case of atomic fluids is often debated as it was initially established in the case of a big Brownian particle immersed in a fluid. Especially, the question is raised to properly define the hydrodynamic radius entering the formula, as well as the constant depending on the boundary conditions at the surface of the particle. In this study, we use our results of viscosity and self-diffusion coefficient obtained by molecular dynamics simulations in the case of alkali metals and their alloys to evaluate the applicability of Stokes-Einstein relation in the case of these liquids. In the case of pure metals, its validity is discussed over a wide range of thermodynamic states, from ambient pressure up to several gigapascals. In the case of alloys, the evolution of its accuracy as a function of temperature and composition is considered. Both definitions of hydrodynamic radius and boundary conditions constant are examined.

Alkali Metal Di-tert-butyl Phosphates: Single-Source Precursors for Homo- and Heterometallic Inorganic Phosphate Materials.

The reaction of alkali metal acetates, M(OAc)·nH2O (M = Li, Na, K), with thermally and hydrolytically unstable di-tert-butylphosphate ((tBuO)2PO2H, dtbp-H) in a 1:1 molar ratio in MeOH at room temperature leads to clean formation of group 1 metal phosphates [Li(μ-dtbp)]n (1), [Na(μ-dtbp)]n (2), and [K4(μ-dtbp)4(μ-H2O)3]n (3). All three compounds are essentially M/L 1:1 complexes. Owing to the presence of larger potassium ions, additional coordinated water molecules are found in 3, which has been further employed as a precursor for the synthesis of a mixed-metal phosphate polymer [CaK(μ-H2O)3(μ-dtbp)3]n (4) by reacting 3 with Ca(OAc)2. Compounds 1-4 have been characterized by various analytical and spectroscopic techniques. Molecular structures of 1-4 have been established in the solid state by single-crystal X-ray diffraction studies, which reveal them to be one-dimensional polymers, where the adjacent metal centers are connected through -O-P-O- bridges formed by the dtbp ligand. These complexes are rare examples of analytically pure alkali metal alkyl phosphates bearing no additional N-donor ligands (other than dtbp ligands, only water molecules are coordinated to the metal centers). Therefore, these compounds can be employed as single-source precursors (SSPs) for nano-sized ceramic phosphates. The thermogravimetric analysis of 1-4 reveals the loss of thermally labile tert-butyl substituents of the organophosphate ligands to form organic-free phosphate materials in the temperature range 300-500 °C. Solvothermal decomposition of 1-3 in boiling toluene leads to the formation of corresponding dihydrogen phosphates M(H2PO4) (M = Li, Na, and K). The thermal decomposition of heterometallic 4 in the temperature range 400-800 °C leads to the formation of phase-pure mixed-metal calcium potassium metaphosphate CaK(PO3)3.

Thermodynamics of equilibrium alkali plasma. Simple and accurate analytical model for non-trivial case

Analytical equation of state for pure alkali metals (lithium, sodium, potassium, rubidium and cesium) in equilibrium gas phase is proposed. This equation has a simple form, generalizes the equation of state for a perfect gas and is universal for all alkali elements. It correctly reproduces the experimental data for the equilibrium gas phase over a wide range of pressures (up to ∼105 Pa) and temperatures (up to ∼3⋅103 K). On the basis of this equation of state, expressions for thermal and caloric coefficients as well as for other physical characteristics are obtained. The results of this study confirm feasibility of the principle of corresponding states in relation to the group of alkali elements.

Binder-free 3D flower-like alkali doped- SnS2 electrodes for high-performance supercapacitors

Tin disulfide can be a good electrode material in supercapacitors due to the presence of significant interlayer space in crystalline structures and large surface area. However, there are only a few reports of its supercapacitor applications. In this study, we report flower-like pure SnS2 and alkali metals (Li, Na, K and Cs) doped-SnS2 nanostructures synthetized by simple single-step solvothermal method without use of any surfactants. Results show that due to the presence of dopants, with increasing radius of the dopant element, the interlayer distance and dislocation intensity increase. This leads to an increase in the expanded space between interlayer and electro-active sites, and therefore, it is possible to intercalate more ions from the electrolyte. But due to the higher conductivity of Na than the other alkali metals, Na doped-SnS2 shows higher current density at constant voltage and thus better capacitance performance than the others. Na doped-SnS2 exhibits higher supercapacitor performance with a high capacitance of 269 Fg−1 at a current density of 1 Ag−1. The significant electrochemical performance of Na doped-SnS2 can be attributed to its particularly good surface area due to the expansion of interlayer space, increasing of electro-active sites and greater conductivity due to the presence of Na.

Sodium-potassium system at high pressure

Mixtures of sodium and potassium differ substantially from the pure elements, while retaining the high compressibility, which is important to the complex behavior of dense alkali metals. We present powder x-ray diffraction of mixtures of Na and K compressed in diamond anvil cells to 48 GPa at 295 K. This reveals two stoichiometric intermetallics: an ${\mathrm{Na}}_{2}\mathrm{K}$ phase known at ambient pressure and low temperature, and a novel NaK phase formed of interpenetrating sodium and potassium diamond lattices. Density functional theory calculations find the new phase to be dynamically stable and, in contrast to pure alkali metals, reveal decreasing electron localization with applied pressure. Depending on the mixture composition these intermetallics are accompanied by sodium or potassium rich phases suggesting that there are no other intermetallics under the range of P-T conditions studied. Alkali-metal mixtures have seen little study at high pressure and represent an unusual class of materials with very high compressibility and multiple constituents. Such materials exhibit significant compression at experimentally accessible pressures and open a way to measure multispecies structures at high compression. These results challenge structural finding algorithms for mixtures in high-pressure conditions.

Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB3 H8 (M=K, Rb, and Cs), Mechanisms of Formation, and the Crystal Structure of KB3 H8.

A facile synthesis of heavy alkali metal octahydrotriborates (MB3 H8 ; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH3 , does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH4 /NaBH4 with THF⋅BH3 have to be carried out under reflux. The high stability and solubility of KB3 H8 were examined, and a crystal structure thereof was obtained for the first time.

Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB3H8 (M=K, Rb, and Cs), Mechanisms of Formation, and the Crystal Structure of KB3H8

AbstractA facile synthesis of heavy alkali metal octahydrotriborates (MB3H8; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH3, does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH4/NaBH4 with THF⋅BH3 have to be carried out under reflux. The high stability and solubility of KB3H8 were examined, and a crystal structure thereof was obtained for the first time.

Characterization of alkali-metal vapor cells fabricated with an alkali-metal source tablet

Optically pumped magnetometers (OPMs) that use alkali metal vapor cells can measure weak magnetic fields generated by the human body. A multichannel detector head with alkali-metal vapor cells mounted in arrays is employed to assure spatial resolution for real-time biomagnetic imaging of various body surfaces. However, further development of alkali metal vapor cell fabrication processes is required to obtain cells with uniform magnetic field sensitivities together with sufficient sensitivity of each individual cell. Herein, the authors propose the fabrication of alkali metal vapor cells for OPM arrays using alkali metal source tablets (AMSTs) as alkali metal dispensers. An AMST is a three-dimensional microstructure that contains precise quantities of the chemical precursors that are used to produce pure alkali metals by low temperature thermal decomposition and to fill reproducible quantities of these metals into cells. In this work, the K production efficiency was characterized with respect to the particular chemical precursors and AMST microstructure employed, and the potential of K-filled glass cells fabricated using AMSTs as components of OPM arrays was demonstrated. An AMST composed of KN3 deposited on porous alumina with 60 μm pore sizes exhibited the most efficient performance during the fabrication of K-filled glass cells. The magnetometric sensitivity obtained with eight K-filled cells was found to be in the range of 3.3–3.8 fTrms/Hz1/2 at a resonance frequency of 10 kHz.

The design of new high energy density materials based on CALYPSO method

High energy density materials (HEDM) have attracted more and more attention due to their wide potential applications as propellants and explosives. Among the family of HEDM, polymeric nitrogen has become a hot topic because its emission is nitrogen gas and is considered as a green and environmentally-friendly HEDM. In this field, the key issue is searching for polymeric nitrogen that can stably exist in ambient conditions. CALYPSO is an efficient structure prediction method based on particle swarm optimization algorithm, which only requires chemical composition can get stable or metastable structures at given conditions. Using CALYPSO technology companied by first-principles calculations, the high-pressure behaviors, including phase transition and electronic properties, of pure nitrogen and alkali metal azides MN3 (M=Li, Na, K, Rb, Cs) have been studied. Based our previous works and some works done by other researchers, we summarized structural evolution and electronic properties of pure nitrogen and MN3 under high pressure in this review. The CALYPSO combining density functional theory (DFT) has predicted a cagelike diamondoid nitrogen with striking stabilization above 263 GPa, named diamondoid N. The diamondoid N adopts a highly symmetric body-centered cubic structure with 20 nitrogen atoms in a unit cell. Alkali metal azides consist of metal cations M+ and linear anions N3-. The anions N3- with double bonds N=N is expected to form polymeric structure at lower pressure comparing to N2 gas due to their lower bonding energy relative to N≡N in N2. Under pressure region 0-400 GPa, the N3- have a series of structural transitions from N3- to pseudo-benzene N6 ring and then to polymeric nitrogen with different structure depending on the alkali metal cations. The structural transition of N3- is companied by hybridization type of nitrogen atoms from sp, sp2 to partial sp3 induced by pressure. Under high pressure, metal elements in azides play two roles. On the one hand, metal atoms act as additives to nitrogen leading to chemical pre-compression effects, which is expected to decrease synthesis pressure of polymeric nitrogen. On the other hand, they act as electronic donors, which is expected to improve the stability of polymeric nitrogen.

Equation of state and artificial neural network to predict the thermodynamic properties of pure and mixture of liquid alkali metals

A statistical mechanical equation of state is developed to predict the volumetric properties of pure and mixture liquid alkali metals at different temperatures, pressures and compositions. The temperature dependent parameters of the equation of state have been calculated using corresponding states correlation based on the normal boiling point parameters as scaling constants. It is shown that the knowledge of just normal boiling point and its liquid density are sufficient to estimate the thermodynamic properties of pure and mixture liquid alkali metals in different conditions. Besides, the performance of artificial neural network (ANN) based on back propagation training with 10 neurons in hidden layer for prediction of behavior of presented systems was investigated. A collection of 512 data points for above systems in different temperatures and pressures was used. The Tao–Mason equation of state (TM EOS) and ANN model results have good agreement with the experimental data with absolute average deviations of 0.74% and 0.299%, respectively.

Thermodynamic properties of two mixed alkali metal borates with NLO behaviour: Li6Rb5B11O22 and Li4Cs3B7O14

Two pure mixed alkali metal borates with Non-Linear Optical (NLO) properties, Li6Rb5B11O22 and Li4Cs3B7O14, have been synthesized by a high-temperature solid state reaction, and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Li6Rb5B11O22 and Li4Cs3B7O14 in 1mol·dm−3 HCl (aq), and of LiCl·H2O(s) in (1mol·dm−3 HCl+H3BO3+RbCl/CsCl) (aq) have been determined by microcalorimeter at T=298.15K, respectively. From these data and with the incorporation of the previously determined enthalpy of solution of H3BO3(s) in 1mol·dm−3 HCl (aq), together with the use of the standard molar enthalpies of formation for LiCl·H2O(s), RbCl(s)/CsCl(s), H3BO3(s), HCl(aq) and H2O(l), the standard molar enthalpies of formation of −(11173.1±9.5)kJ·mol−1 for Li6Rb5B11O22 and −(7145.1±5.9)kJ·mol−1 for Li4Cs3B7O14 were obtained on the basis of the appropriate thermochemical cycles.

A new equation of state for molten alkali metal alloys

A new proposed equation of state (EoS) for pure liquid alkali metals has been extended to predict the volumetric and thermodynamic properties of alkali metal alloys at different temperatures, pressures, and compositions. The new equation which is valid over the whole liquid range is based on a suggested potential function and the interactions of nearest neighbors are according to the characteristics of the soft repulsive interaction in dense and large attractive interaction in expanded liquid alkali metals. The composition dependencies of the parameters of the equation of state are assumed as quadratic functions of mole fraction considering the mean geometry approximation “MGA”. In this paper, the calculated results of liquid density and other thermodynamic properties such as isobaric expansion coefficient, αP, isothermal compressibility, κT, and internal pressure, Pi, of binary molten alloys of Na–K and Cs–K from the freezing point up to several hundred degrees above the boiling point are presented. The results show good agreement between the density values obtained from this equation and the experimental and literature data. To show the ability of this EoS in prediction of density of alkali metal alloys, the results have been compared with some other equations. Although there is no corresponding literature data to compare the results obtained for derived thermodynamic properties, the variations of these properties with temperature and composition show proper trends for these alloys.

Equation of state for thermodynamic properties of pure and mixtures liquid alkali metals

We developed an equation of state based on statistical–mechanical perturbation theory for pure and mixtures alkali metals. Thermodynamic properties were calculated by the equation of state, based on the perturbed-chain statistical associating fluid theory (PC-SAFT). The model uses two parameters for a monatomic system, segment size, σ, and segment energy, ɛ. In this work, we calculate the saturation and compressed liquid density, heat capacity at constant pressure and constant volume, isobaric expansion coefficient, for which accurate experimental data exist in the literatures. Results on the density of binary and ternary alkali metal alloys of Cs–K, Na–K, Na–K–Cs, at temperatures from the freezing point up to several hundred degrees above the boiling point are presented. The calculated results are in good agreement with experimental data.

Catalytic effect of black liquor on the gasification reactivity of petroleum coke

CO 2 gasification of petroleum coke using black liquor as a catalyst was performed in a thermogravimetric analyzer (TGA) under temperatures 1223–1673 K at ambient pressure to evaluate the effect of black liquor loading on petroleum coke gasification. It was found that the gasification reactivity of petroleum coke was improved greatly by black liquor. The gasification reactivity was affected by different loading methods in the order: wet grinding > dry grinding > physical impregnation > dry mix. The catalytic activity of black liquor was higher than that of pure alkali metal. The effect of temperature on the gasification reactivity of petroleum coke was changed by black liquor. The reactivity reaches its maximum at 1573 K. The reactivity of petroleum coke was found higher than that of Shenfu coal when black liquor loading is 5 wt.% (of petroleum coke), clearly demonstrating that black liquor could be an effective catalyst for petroleum coke gasification.

Analysis of High Efficiency Electromagnetically Induced Transparency in Potassium Vapor

We present a rate-equation theoretical model describing the optical pumping processes on the K D1 line and we then discuss their influence on the electromagnetically induced transparency resonance parameters. We present also a comparison with the results of an experiment performed in cells containing pure alkali metal or added with a few torrs of buffer gas. The model shows that, in the last case, the complete Maxwellisation of the atomic population velocity distribution, along with the overlapping Doppler profiles of the transitions from the ground-states typical of K, leads to a partial compensation of optical pumping and a significant increase of the amplitude of the electromagnetically induced transparency resonances.

Phonon dispersion in alkali metals and their equiatomic sodium-based binary alloys

In the present article, the theoretical calculations of the phonon dispersion curves (PDCs) of five alkali metals viz. Li, Na, K, Rb, Cs and their four equiatomic sodium-based binary alloys viz. Na0.5Li0.5, Na0.5K0.5, Na0.5Rb0.5 and Na0.5Cs0.5 to second order in a local model potential is discussed in terms of the realspace sum of the Born von Karman central force constants. Instead of the concentration average of the force constants of pure alkali metals, the pseudo-alloy-atom (PAA) is adopted to directly compute the force constants of the four equiatomic sodium based binary alloys and was successfully applied. The exchange and correlation functions due to the Hartree (H) and Ichimaru-Utsumi (IU) are used to investigate the influence of the screening effects. The phonon frequencies of alkali metals and their four equiatomic sodium-based binary alloys in the longitudinal branch are more sensitive to the exchange and correlation effects in comparison with the transverse branches. The PDCs of pure alkali metals are found in qualitative agreement with the available experimental data. The frequencies in the longitudinal branch are suppressed rather due to IU-screening function than those due to static H-screening function.

Concentration fluctuations in liquid alloys of alkali metals

Large-scale molecular dynamics simulations are performed to study the structure of liquid alloys of alkali metals (namely K–CS, Na–K, and Na–Cs) on the whole range of composition. The interactions are described by Fiolhais’ pseudopotential that has already proven its ability to describe the interactions in pure liquid alkali metals. By a comparison of the total structure factor with experimental results, the transferability of the description of the interactions is ascertained for all these systems on the whole composition range. Since these systems exhibit different behaviors at the level of the composition fluctuations, partial pair distribution functions and Bathia–Thornton’s partial structure factors are displayed for some representative compositions. The influence of the characteristics of the interactions on these fluctuations is examined. Size mismatch as well as energetic non-additivity favor heterocoordination while the attraction asymmetry encourages homocoordination. A competition between these two effects is pointed out.

How Can We Make Stable Linear Monoatomic Chains? Gold-Cesium Binary Subnanowires as an Example of a Charge-Transfer-Driven Approach to Alloying

On the basis of first-principles calculations of clusters and one dimensional infinitely long subnanowires of the binary systems, we find that alkali-noble metal alloy wires show better linearity and stability than either pure alkali metal or noble metal wires. The enhanced alternating charge buildup on atoms by charge transfer helps the atoms line up straight. The cesium doped gold wires showing significant charge transfer from cesium to gold can be stabilized as linear or circular monoatomic chains.