碱金属Cs和Na与GaAs(100)界面相互作用的光电子能谱研究

用光电子能源谱技术（XPS和UPS）研究了金属Cs和Na与GaAs（100）的界面形成。实验结果表明，Cs和Na吸附在GaAs（100）表面时，衬底As向外扩散，形成混合相。在Na吸附的表面，As扩散程度比Cs吸附的表面大。随着复盖层厚度增加，吸附层开始金属化。     

The effects of alkali impurities on the superconductivity and powder characteristics of YBa2Cu3O7

The effects of alkali impurities, Li, Na, K, Rb, and Cs, on the superconducting properties and powder characteristics of YBa₂Cu₃O₇ were investigated. The superconducting temperature of YBa₂Cu₃O₇ drops to the 70 K range in the presence of Li (0.2 mole Li/mole 1-2-3 oxide), while samples containing Rb, K, or Cs show little superconductivity deterioration. An intermediate effect between these two extremes was found for Na. The powder characteristics, inlcuding aggregate hardness, particle size, and particle morphology, of YBa₂Cu₃O₇ are also affected by the alkali impurities. In particular, during calcination both Li and Na enhance the intergrain bonding, resulting in increased difficulty in power comminution, while K and particularly Rb have the opposite effect.     

Behavior of Alkali Metal and Ammonium Salts in Nanofiltration of Their Aqueous Solutions

Radiochemistry - The behavior of salts (chlorides, nitrates, sulfates, phosphates, borates, ferri- and ferrocyanides) of various alkali metals (Li, Na, K, Cs) and ammonium in the course of...     

A comparative study of electrical resistivity of liquid alkali metals

The resistivities of liquid alkali metals are investigated using Ziman formula and the alternative expression based on Kubo formula suggested by Ünal and Alkan [B. Ünal, B. Alkan, J. Phys. Soc. Jpn. 62 (1993) 2425]. As the input pseudopotential, the individual version of the electron-ion potential proposed by Fioalhais and coworkers which was originally developed for solid state is used and static structure factors are derived from the solution of Ornstein–Zernike integral equation with Rogers–Young closure. Good agreement with experiment is found for liquid Na and K using both formulas. For Li, Rb and Cs the agreement between the calculated values using Ziman formula and experimental data is less satisfactory. From present investigations, it is shown that the formula based on Kubo formula suggested by Ünal and Alkan is the better chose for the resistivity calculations of liquid Li, Rb and Cs metals.     

MAEAM Investigation of Phonons for Alkali Metals

Within the harmonic approximation, the atomic force constants have been derived and the phonon dispersion curves along three major symmetry directions [00ζ], [0ζ ζ] and [ζ ζ ζ] (or in group-theory notation Δ, Σ, and Λ) have been calculated for five alkali metals Li, Na, K, Rb and Cs by combining the modified analytic embedded atom method (MAEAM) with the theory of lattice dynamics. The results are in agreement with available experimental results for Li, Na and K, which may imply that the predicted phonon dispersion curves for Rb and Cs are correct.      

Viscosity and thermal conductivity of binary eutectics of alkali metals in the vapor phase

Values calculated for the dynamic viscosity and thermal conductivity are presented for vapors of binary eutectics of the alkali metals at temperatures from 800 to 1500 K and at pressures from 100 to 8×10⁵ Pa. Data are presented for the vapors of the systems Li + Na, Na + Rb, Na + Cs, K + Rb, K + Cs, Na + K, and Rb + Cs. The values of the concentrations of the five components in the vapor phase of each binary eutectic are also presented. The accuracy of the calculated viscosities is estimated to be within 4–5% and the accuracy of the calculated thermal conductivities is estimated to be within 8–10%.     

Linear Isotherm for Compressed Molten Alkali Metals

Molten alkali metals are shown to be in the domain of the newly developed linear regularity that is valid for pure compressed liquids and liquid mixtures. It holds in the range of melting to boiling temperature and shows deviations as the critical temperature is approached. The agreement with experimental data is better than 1.4% when it is used to predict the density of molten Li, Na, K, Rb, and Cs metals. A reasonable conformity with the ISM statistical mechanical equation of state is manifested.     

Non-isovalent metal substitution for bismuth,strontium, calcium,and copper in bi-based 2212 superconducting ceramics

The aim of this paper is to investigate the influence of non-isovalent alkali (Li, Na, K, and Cs) substitution in Bi₂Sr₂CaCu₂O₈, in particular on its synthesis conditions and on their resistive and thermopower electrical properties. Liquid phase development during the synthesis process leads to the formation of sintered materials at a lower temperature compared to the undoped 2212 compound. The final composition is discussed as a function of which crystallographic site is partially substituted. The presence of alkali ions in the initial chemical composition leads to improved electrical properties. Such data are correlated with the microstructure and chemical composition of the end-product.     

Relative sensitivity factors for alkali metal and ammonium cations in single-particle aerosol time-of-flight mass spectra

A variety of factors have been investigated with regard to the quantitation of chemical species within individual ambient aerosol particles analyzed by laser desorption time-of-flight mass spectrometry. Spectrum to spectrum differences in the interaction of the particle with the ionization laser beam, which affect the absolute peak areas in the mass spectra, can be minimized by using relative peak areas instead of absolute peak areas in each spectrum. Whereas absolute peak areas vary by an average of 59% for a given ion peak in single particle mass spectra of a monodisperse aerosol of particles formed from the same solution, relative peak areas in the same mass spectra vary only by an average of 16%. Relative sensitivity factors (RSF) relating the mass spectral ion intensity of NH4+ and the alkali metal cations Li+, Na+, K+, Rb+, and Cs+ in single particle aerosol time-of-flight mass spectrometry to their bulk concentrations have been determined. The values for Li+/Na+, K+/Na+, Rb+/Na+, Cs+/Na+, and NH4+/Na+ are found to be 0.14, 5.1, 6.0, 7.9, and 0.014, respectively. The higher response for heavier cations of the alkali metals is consistent with the periodic trends of both ionization potential and lattice energies of the species of interest. The response factor for sodium and potassium cations has been used to accurately determine the relative amounts of Na+ and K+ in sea-salt particles, by analyzing a sample of approximately 360 ambient sea-salt particles. The relative amounts of Na+ and K+ are found to be 97 and 3% in particles, respectively, whereas in seawater they are, on average, 98 and 2%.     

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. Na_0.5Li_0.5, Na_0.5K_0.5, Na_0.5Rb_0.5 and Na_0.5Cs_0.5 to second order in a local model potential is discussed in terms of the real-space 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.     

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. Na_0.5Li_0.5, Na_0.5K_0.5, Na_0.5Rb_0.5 and Na_0.5Cs_0.5 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.     

Melt-assisted phase transformations of A/W/Mn/SiO<Subscript>2</Subscript> (A = Li,Na, K,Rb, Cs) composite catalysts

This paper analyzes results obtained in studies of A/W/Mn/SiO₂ (A = Li, Na, K, Rb, Cs) composite catalysts for the oxidative coupling of methane (OCM). Particular attention is paid to phase transformations. It is pointed out that the SiO₂ matrix is an active catalytic component of the composites, rather than an inert carrier of additives, and that the heterogeneous OCM process involves melts based on alkali metal tungstates, along with polycrystalline manganese oxides. The effects of the cation ratio and synthesis method on the phase composition of the A/W/Mn/SiO₂ (A = Li, Na, K, Rb, Cs) materials is examined.     

Thermodynamic characteristics of vaporization of alkali metals

The saturation vapor of an alkali metal is treated as a monatomic particle real gas whose volumetric behavior is described by a truncated form of virial equation. The condensed state-vapor equilibrium constant, equal to the saturation fugacity for Li, Na, K, and Cs, is determined through evaluation of the second virial coefficient's temperature dependence. The third and the second law values of standard enthalpy of vaporization at the reference temperature 298 K for the same metals are determined. The applied procedure for evaluation of the second virial coefficient's temperature dependence produced small deviations for the resulting second law values and gave mean values in good agreement with literature data, especially with those of the JANAF Tables.     

A Ternary Hybrid-Cation Room-Temperature Liquid Metal Battery and Interfacial Selection Mechanism Study

The dendrite-free sodium–potassium (Na–K) liquid alloy composed of two alkali metals is one of the ideal alternatives for Li metal as an anode material while maintaining large capacity, low potential, and high abundance. However, Na- or K-ion batteries have limited cathode materials that can deliver stably large capacity. Combining advantages of both, a hybrid-cation liquid metal battery is designed for a Li-ion-insertion-based cathode to deliver stable high capacity using a Na–K liquid anode to avoid dendrites. The mechanical property of the Na–K alloy is confirmed by simulation and experimental characterization, which leads to stable cycling performance. The charge carrier selection principle in this ternary hybrid-cation system is investigated, showing consistency with the proposed interfacial layer formation and ion distribution mechanism for the electrochemical process as well as the good stability. With Li ions contributing stable cycling as the cathode charge carrier, the K ion working as charge carrier on the anode, and Na as the medium to liquefy K metal, such a ternary hybrid battery system not only inherits the rich battery chemistry of Li-insertion cathodes but also broadens the understanding of alkali metal alloys and hybrid-ion battery chemistry.     

Vapor synthesis of alkali metal-TCNQ salt films

Alkali metal salts of the radical anion of the organic acceptor 7,7,8,8-tetracyanoquinodimethan (TCNQ) have been synthesized from neutral TCNQ and the elemental alkali metals by means of a vapor reaction technique. Using this method thin, polycrystalline films of the simple (1:1) salts of Li, Na, K, and Rb were prepared as well as films of the complex (2:3) salt of Cs. X-Ray powder diffraction data for these materials are presented and compared with data obtained both from materials synthesized by conventional solution reactions and from known crystal structure data. The ultraviolet photoemission spectrum of NaTCNQ was found to correlate very well with that previously reported for KTCNQ.     

Facilitated transfer of alkali-metal cations by dibenzo-18-crown-6 across the electrochemically polarized interface between an aqueous solution and a hydrophobic room-temperature ionic liquid

The facilitated transfer of alkali metal cations (Li+, Na+, K+, Rb+, Cs+) by dibenzo-18-crown-6 (DB18C6) across the electrochemically polarizable interface between an aqueous solution (W) and a hydrophobic ionic liquid, N-octadecylisoquinolinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ([C18Iq][TFPB]), has been studied using cyclic voltammetry at the interface formed at the tip of a micropipet. In cyclic voltammograms (CVs), the current due to the facilitated transfer of the cations by DB18C6 from W to [C18Iq][TFPB] can be measured within the polarized potential window of the [C(18)Iq][TFPB]|W interface. The stoichiometry of the complexes in [C18Iq][TFPB] for Li+, Na+, K+, and Rb+ are found to be 1:1 while for the Cs+ transfer both 1:1 and 1:2 complexes are likely to be formed. The formation constants of the 1:1 complexes for Li+, Na+, K+, and Rb+ in [C18Iq][TFPB], , evaluated from CVs are log = 5.0, 7.0, 8.2, and 7.3, respectively. The value for K+ is 1 order of magnitude greater than that for Na+. This higher selectivity of DB18C6 to K+ over Na+ in [C18Iq][TFPB] compared with that in molecular solvents suggests that the RTIL provides a unique solvation environment for the complexations of DB18C6 with the ions.     

Surface modification of poly(tetrafluoroethylene) by magnesium amalgam

Mg amalgam reacts with PTFE (foil or oriented film on Si) to give a thin surface layer containing MgF₂ in a mixture with complicated, air-sensitive, carbonaceous product containing large amount of residual C-F bonds. The reaction does not propagate into the bulk polymer, which, consequently, retains its white color even after hundreds of hours of reaction at 150 °C. These findings contrast with the reactivity of PTFE with amalgams of alkali metals, Li, Na, K. The differences are interpreted, in terms of the electrochemical model of amalgam carbonization, as blocking of charge (e^–/Mg ²⁺) propagation through the modified layer. AFM patterns show that the Mg-treatment increases the surface roughness. The molecular-level ordering of PTFE films is strongly perturbed by the action of Mg-amalgam; the treated surface shows only small proportion of organized macromolecules.     

Experimental investigation on the influence of the presence of alkali compounds on the performance of a commercial Pt–Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> diesel oxidation catalyst

Experimental investigation was conducted on the influence of the presence of alkali compounds such as K and Na present in biofuels on catalytic behaviors of a commercial diesel oxidation catalyst (Pt/Pd/Al₂O₃) in the monolith form. Doping of different alkali metal components on carrots of monolith was performed. These carrots were physicochemically characterized, and the catalytic tests consisted of series of temperature-programmed surface reactions with representative exhaust gas mixtures from diesel combustion. The aim of the present study is to reveal the effect of the alkali metal on overall catalytic activity of diesel oxidation catalyst (DOC) and more particularly to show their influence on the reactions involving CO, hydrocarbons, NO, and NO₂. Potassium and sodium lead to different catalytic properties. A promotion effect was found in the presence of K, whereas an inhibiting effect was evidenced in the presence of Na or when both Na and K were doped onto the DOC.     

Thermochemistry of Alkali Metal Uranoborates and Their Crystal Hydrates

The standard enthalpies of formation at T = 298.15 K were determined for A^IBUO₅·nH₂O (A^I = Li, Na, K, Rb, Cs). The heat capacity of crystalline NaBUO₅·H₂O was determined by adiabatic vacuum calorimetry, and its thermodynamic functions were calculated. The thermodynamic characteristics of dehydration of alkali metal uranoborates were evaluated.     

Investigation of magnetic properties and microstructure of ultrathin Co films grown on Si(111)- 7 x 7 surface

Magnetic properties and growth mechanism of ultrathin Co films on Si(111)-7 x 7 surface have been studied by using both surface magneto-optic Kerr effect (SMOKE) and scanning tunneling microscopy (STM), respectively. STM results show that the growth mechanism of ultrathin Co films on Si(111)-7 x 7 surface at room temperature belongs to Stranski-Krastanov (SK) growth mode. Due to formation of CoSi2 layer, no magnetic signal could be detected by SMOKE for 1-4 ML Co deposited on Si(111) surface. Because of rougher surface, both longitudinal and perpendicular magnetic anisotropy configuration appear for 4.2-10 ML Co/Si(111) films. When the Co thickness is increased to 10 ML, only longitudinal anisotropy configuration is found, resulting from the contribution to the volume anisotropy. Furthermore, in-plane coercivity increases with Co coverage because of enhancement of ferromagnetic coupling with Co thickness, out-of-plane coercivity increases with Co coverage due to the increment of demagnetized field, induced by the rougher Co surface and pinhole structures.