Microscopic investigation of ionic conductivity in alkali metal salts-poly(ethylene oxide) adducts

We present conductivity, N.M.R. and D.S.C. measurements in two P(EO) complexes : P(EO) ₈LiCF₃SO₃ and P(EO) ₁₀NaI. From N.M.R. experiments, we deduce the respective amount of crystalline and elastomeric phases at all temperatures, as well as the salt concentration in these various phases. The elastomeric phase is shown to be responsible of the ionic conductivity at all temperatures, and to be very dilute (n ? 25 just above the pure P(EO) melting point. The high melting salt-rich complexes are found surstoechiometric (n ? 3.5). The various factors affecting the temperature dependence of the conductivity are discussed, as well as the kinetics problems.     

Hofmeister series and ionic effects of alkali metal ions on DNA conformation transition in normal and less polarised water solvent

Normal and less polarised water models are used as the solvent to investigate Hofmeister effects and alkali metal ionic effects on dodecamer d(CGCGAATTCGCG) B-DNA with atomic dynamics simulations. As normal water solvent is replaced by less polarised water, the Hofmeister series of alkali metal ions is changed from Li⁺ > Na⁺ ? K⁺ ? Cs⁺ ? Rb⁺ to Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺. In less polarised water, DNA experiences the B→A conformational transition for the lighter alkali metal counterions (Li⁺, Na⁺ and K⁺). However, it keeps B form for the heavier ions (Rb⁺ and Cs⁺). We find that the underlying cause of the conformation transition for these alkali metal ions except K⁺ is the competition between water molecules and counterions coupling to the free oxygen atoms of the phosphate groups. For K⁺ ions, the ‘economics’ of phosphate hydration and ‘spine of hydration’ are both concerned with the DNA helixes changing.     

An ESCA study of tin (IV) and tin (II) chelates with substituted 8-quinolinols

X-ray photoelectron spectra of several solid tin (IV) and tin (II) chelates with substituted 8-quinolinols have been recorded. An Sn 3d_{$\text{5}\text{2}$} binding-energy range of 2.96eV is found. Qualitative analysis of the results shows that there seems to be no apparent correlation between the Sn 3d binding energy and the coordination numb     

碱金属原子和类氢离子束缚态能级的解析解

对于碱金属原子和类氢离子的原子实模型,从物理实质图像和极化与贯穿作用的量化及实验资料入手深入地进行了分析,引入了半经验碱金属和类氢原子内部相互作用势,建立了定态薛定谔方程.运用微扰理论获得能级Enl,并进一步导出了有效主量子数、有效核电荷数等重要参数.这对物质化学特性和原子特性研究是有益的.     

Chemical transport reactions in the In-Sn-S ternary system: Existence of tin (II) and tin (IV) atoms by Mössbauer effect of119Sn in the isolated compounds

Iodine vapour transport, carried out in the In-Sn-S ternary system leads to single crystals with quite different morphologies: needles, sticks, sheets and polyhedra. The two oxidation states of tin atoms are shown for all these phases by¹¹⁹Sn Mössbauer effect. A varying relative proportion of tin(IV) — tin(II) is observed according to the different crystal forms.     

On the transport of activated particles by flow and diffusion

It will be shown, how the spatial decay of active molecules — excited electronically or activated otherwise (e.g., chemical processes) is determined by diffusion and flow as well as by the intrinsic molecular constant. The exact analysis in cylindric geometry leads to a set of unique solutions, which in lowest order are characterized by a weak gradient of the particle concentration at the wall and a pronounced kernel in the center of the tube. In special cases there exists a simple but powerfull expansion of any distribution in the source, which are very similar to Fourier-Bessel series. The solutions in lowest order will be used to analyze the measured decay of activated oxygen in a steady stream of molecular oxygen. Since the decay constant is determined by volume deactivation and by the removal of particles at the wall, evaluation of experimental data, however, remains necessarily ambiguous.     

Reflection spectra of (alkali metal,thallium (I), silver (I)) iridium (IV) hexachlorides

While the effect of rubidium and caesium ions in solid salts of IrCl₆ ^-- is a shift to lower wave-numbers, comparable to that occurring in organic solvents relative to water, the dark blue silver (I) and thallium (I) salts have a new, broad band in the red. Mixed crystals of Cs₂IrCl₆ and Tl₂IrCl₆ are prepared, and the absorption spectra are discussed in terms of a tendency to ‘ferroelectric rattling’ and strong covalent bonding of Ag and Tl. Analogous cases are pointed out in solid salts of other 5d-hexahalides.     

Application of synchrotron radiation to investigation of the mechanism of increase in the yield of alkali metal ions in electron-stimulated desorption

Core-level photoelectron spectroscopy with synchrotron radiation (hv = 140 eV) has been applied to study the variation in the Si⁺ charge state in silicon films deposited on the W(100) surface after thermal annealing of the substrate. The purpose of this study is to check the mechanism responsible for the sharp increase in the yield of Na⁺ ions in electron-stimulated desorption from a sodium layer adsorbed on the Si/W(100) surface after high-temperature annealing. The evolution of the W 4f _7/2 and Si 2p photoelectron spectra and the valence band photoemission spectra is investigated for two silicon coverages (1 and 3 ML) on the W(100) surface in the temperature range 300<T<2200 K. It is shown that annealing of 1 ML Si on the W(100) surface results in the formation of a W-Si covalent bond, which can weaken the Si-Na bond and lead to an increase in the equilibrium distance X ₀ and, hence, to an increase in the yield of Na⁺ ions in electron-stimulated desorption. The variation in the photoelectron spectra under annealing of 3 ML Si differs from that observed after annealing of 1 ML Si in the direction of charge transfer, thus correlating with the opposite effect of annealing of 3 ML Si/W on the Na⁺ yield in electron-stimulated desorption.     

The relationship between chemical and tracer diffusion coefficients of aliovalent ions in an ionic lattice

The theoretical model developed by Lidiard was extended to describe the relationship between the chemical and tracer diffusion coefficients of aliovalent ions in an ionic lattice.It is shown that the relationship between the chemical diffusion coefficient, D, and the tracer diffusion coefficient, D¹, is D = 2D¹ if the migration of dimers is the principal mechanism of transport and for the migration of trimers D = 3D¹ if the concentration of impurity ion is relatively small. These relationships are valid regardless of the charge of the aliovalent or lattice ions.The chemical diffusion coefficients of Cr³⁺ in Cr-doped MgO were determined for three different temperatures, 1656, 1717 and 1768K, and for the concentration region 2.5×10^?2?2.8×10^?1 mole% Cr₂O₃. Using previously determined values for the tracer diffusion coefficient of ⁵¹Cr in Cr-doped MgO it was found that for the temperature and concentration region investigated D = (2.00±0.17)D¹ which indicates that diffusion proceeds primarily by the migration of dimers.     

Secondary ion emission processes of sputtered alkali ions from alkali/Si(100) and Si(111)

The secondary alkali ion yield vs. the work function change (Δφ) of Na, K and Cs/Si(100) and Si(111) was measured to discuss the details of secondary ion emission processes. In the case of alkali/metal systems, the secondary ion emission is explained by the electron tunneling model. In this model, the ionization of the ejected atom occurs as a result of electron resonant tunneling through the potential barrier separating an atom and a metal, and the secondary ion yield depends on exponentially the work function change of metal surface. For alkali/Si(100) systems, the secondary ion emission processes are explained in terms of the electron tunneling model since the secondary alkali ion yield vs. the work function change (Δφ) follows the exponential manner. However, it is not easy to apply the simple electron tunneling model to our experimental results for alkali/Si(111) systems. There is the essential difference in surface structures between Si(100) and Si(111). Therefore, it is suggested that the local electronic environment around the adsorbates might be taken into consideration for alkali/Si(111) systems.     

Vapor-liquid (insulator-metal) phase transition in alkali metal vapors

A simple physical model is proposed that describes a vapor-liquid phase transition in alkali metal vapors. The model is based on an assumption made on the character of binding between atoms in the gas phase near the critical point. This is the collective quantum cohesive energy, well-known in the theory of liquid alkali metals, which arises due to the appearance of conduction electrons and is extended to the gas region near the critical point. The parameters of the critical points of the transition and of the binodal are determined on the basis of the model calculation of the binding energy for all alkali metals. Combined, these parameters well agree with experimental results and the predictions made by other authors. The minimum metallic conductivity is evaluated. Its behavior allows one to conclude that vapor-liquid and insulator-metal transitions in alkali metal vapors coincide. This fact sheds light on the Zel’dovich-Landau problem as applied to alkali metal vapors.     

On the origin of atomistic mechanism of rapid diffusion in alkali halide nanoclusters

To elucidate the atomistic diffusion mechanism responsible for the rapid diffusion in alkali halide nano particles, called Spontaneous Mixing, we execute molecular dynamics simulations with empirical models for KCl-KBr, NaCl-NaBr, RbCl-RbBr and KBr-KI. We successfully reproduce essential features of the rapid diffusion phenomenon. It is numerically confirmed that the rate of the diffusion clearly depends on the size and temperature of the clusters, which is consistent with experiments. A quite conspicuous feature is that the surface melting and collective motions of ions are inhibited in alkali halide clusters. This result indicates that the Surface Peeling Mechanism, which is responsible for the spontaneous alloying of binary metals, does not play a dominant role for the spontaneous mixing in alkali halide nanoclusters. Detailed analysis of atomic motion inside the clusters reveals that the Vacancy Mechanism is the most important mechanism for the rapid diffusion in alkali halide clusters. This is also confirmed by evaluation of the vacancy formation energy: the formation energy notably decreases with the cluster size, which makes vacancy formation easier and diffusion more rapid in small alkali halide clusters.     

Fast diffusion of copper(I) ions in NaI

Results are presented for nmr investigations into the diffusion of Cu⁺ in NaI. The nmr results show that a considerable amount of the copper(I) ions is incorporated interstitially and that the mean jump frequency ν_Cu of the Cu⁺ ions is much higher than that of the host cations: ν_Cu/ν_Na ≈ 820 at 320 °C. Two values for the temperature dependence of ν_Cu are found: E₁ = 1.63 eV (T < 300 °C) and E₂ = 0.61 eV (T > 300 °C). The nature of the mechanism of the Cu⁺-migration in NaI is discussed and a model proposed. The interstitial incorporation and fast diffusion of the Cu⁺ ions is confirmed by a comparison with the results for CdI₂ doped NaI. CdI₂ is incorporated substitutionally and the mean jump frequency ν_Cd is lower than that of the host ions: ν_Cd < 10⁸ s^-1 at 650 °C.For the pure substance conductivity measurements were performed too, for vomparison. The agreement of nmr and conductivity data is good. From both δH_m = 0.59 eV and δH_s = 2.08 eV were calculated in excellent agreement with recently reported data. It is shown that the presence of oxygen in the samples leads to wrong data. A method for removing this impurity is described.     

Binding of tetrahedral halocomplexes of polyvalent metal ions in an ionic model

Summary Long-lived tetrahedral coordination of polyvalent metal ions by halogen ions is known to be stable in a number of liquid halide mixtures. We evaluate the binding of isolated tetrahedral halocomplexes for the alkaline earth metals and for Al, with the main aim of assessing their stability and their bond length. An appropriate interionic force model is available for the halides of Mg, Ca, Sr and Ba from analyses of cohesion in their crystalline state and in dihalide molecules. The model is extended to the halides of Be and Al with the adjustment of a parameter to the measured Be-F and Al-Cl bond lengths in liquid mixtures. The semi-quantitative usefulness of the model is confirmed by comparisons with bond lengths for other Al halides and with extensive information on local vibrational frequencies from Raman scattering and infrared emission experiments on liquid halides.

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Riassunto è noto che ioni di metalli polivalenti in numerose miscele di alogenuri fusi sono coordinati tetraedricamente da ioni alogeno. Nel lavoro si calcolano le proprietà di legame di complessi tetraedrici isolati formati con gli alogeni dai metalli alcalino-terrosi e dall’Al, con particolare attenzione alla loro stabilità e lunghezze di legame. Si usa a questo scopo un modello ionico derivato per gli alogenuri di Mg, Ca, Sr e Ba da proprietà coesive delle fasi solida e gassosa, estendendolo poi agli alogenuri di Be e di Al. L’utilità semiquantitativa del modello è confermata dal confronto con dati sperimentali per alogenuri liquidi, riguardanti principalmente le frequenze vibrazionali locali da esperimenti di diffusione Raman.

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Резюме Известно, что долгоживущие тетраэдрические комплексы поливалентных металлических ионов, благоларя ионам галогенов, являются стабильными в ряде жидких смесей галогенидов. Мы оцениваем связь изолированных тетраэдрических галокомплексов для щелочноземельных металлов и для Al с целью определения их устойчивости и длины связи. Предлагается соответствующая модель межионной силы для галогенидов Mg, Ca, Sr и Ba из анализа когезии в кристаллическом состоянии и в молекулах дигалогенидов. Эта модель обобщается на случай галогенидов Be и Al с подгонкой параметра по измеренным длинам связи Be−F и Al−Cl в жидких смесях. Полуколичественные результаты модели подтверждаются с помощью сравнения длин для других галогенидов алюминия и с помощью имеющейся информации о локальных колебательных частотах из комбинационного рассеяния и экспериментов по инфракрасномы излучению в жидких галогенидах.