Anisotropie dipole polarizabilities and quadrupole moments of open-shell atoms and ions: O,F, S,Cl, Se,Br and isoelectronic systems

Quadrupole moment and dipole polarizability tensor components are calculated at the correlated complete-active-space self-consistent-field (CASSCF) and complete-active-space perturbation-theory (CASPT) levels for ²P states of O^?, F, Ne⁺, Na²⁺, S^?, Cl, Ar⁺, 98, K²⁺ , Se^?, Br, Kr⁺, Rb²⁺ and ³P, ¹D, ¹S states of O^?, F⁺, Ne²⁺, Na³⁺, S, Cl⁺, Ar²⁺, K³⁺, Se, Br⁺, Kr²⁺, Rb³⁺. Relativistic corrections are included perturbatively for the 34- and 35-electron systems.     

Density functional theory study on the adsorption of alkali metal ions with pristine and defected graphene sheet

The graphene-based materials along with the adsorption of alkali metal ions are suitable for energy conversion and storage applications. Hence in the present work, we have investigated the structural and electronic properties of pristine and defected graphene sheet upon the adsorption of alkali metal ions (Li⁺, Na⁺, and K⁺) using density functional theory (DFT) calculations. The presence of vacancies or vacancy defects enhances the adsorption of alkali ions than the pristine sheet. From the obtained results, it is found that the adsorption energy of Li⁺ on the vacancies defected graphene sheet is higher (3.05?eV) than the pristine (2.41?eV) and Stone–Wales (2.50?eV) defected sheets. Moreover, the pore radius of the pristine and defected graphene sheets are less affected by metal ions adsorption. The increase in energy gap upon the adsorption of metal ions is found to be high in the vacancy defected graphene than that of other sheets. The metal ions adsorption in the defective vacancy sheets has high charge transfer from metal ions to the graphene sheet. The bonding characteristic between the metal ions and graphene sheet are analysed using QTAIM analysis. The influence of alkali ions on the electronic properties of the graphene sheet is examined from the Total Density of States (TDOS) and Partial Density of States (PDOS).     

Energy of migration of monovalent ions in NaCl: An experimental and theoretical study

Experimental diffusion measurements show that migration enthalpies of Cl^?, Br^? and I^? in NaCl are comparable, while that of F^? is considerably lower. Earlier studies had shown that migration enthalpies of Na⁺, K⁺, Rb⁺ and Cs⁺ in NaCl were similar. The polarised point ion model predicts migration energies of ions (by vacancy mechanism) to monotonically increase with ion size, contrary to experiment. Inversely, the shell model calculations rightly predict the variation of migration energies with ionic size. Thus, migration energies by vacancy mechanism do not vary significantly for ions larger than the host ions. However, in the case of the small ions, Li⁺ and F^?, the migration energies by vacancy mechanism are much lower and in good agreement with experiment for F^?.     

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.     

Ionic conductivity and point defects in pure and doped MnF2 and MgF2 single crystals

Conductivity, σ, of MnF₂ and MgF₂ single crystals, pure and doped (with Li⁺, Na⁺, Y³⁺, Gd³⁺), has been measured, from room temperature to 500°C. Further, some crystals were contaminated with O^2? as an additional impurity. These tetragonal (rutile structure) crystals both behave like typical ionic conductors. Of particular interest is the existence of a large anisotropy, σ being largest when measured parallel to the c-axis. Study of the conductivity isotherms and anisotropy as functions of impurity concentration allows identification of the conduction mechanism in terms of the migration of two mobile defects: the fiuorine-ion vacancy, V_F, and interstitial, F_i. A value of 1.44 eV was obtained for the enthalpy of formation of the intrinsic anion Frenkel defect, 0.80 eV for the migration enthalpy of a V_F and 0.88 eV for an F₁ in MnF₂ parallel to the c-axis. Similar values were obtained for MgF₂. This work shows that more information about point defects can be obtained from conductivity measurements in non-cubic cyrstals than in cubic ionic crystals, because of the additional information from conductivity anisotropy.     

Local structure and lattice dynamics of alkali halide crystals with an anion vacancy

The local structure and vibrations in the region of an anion vacancy are studied using the pair interionic potentials within the shell model for crystals Me ⁺Cl^? (Me ⁺ = Rb⁺, K⁺, Na⁺). The pair potentials are derived from first-principles calculations of different clusters by the Hartree-Fock-Roothaan method with the one-electron states constructed in the form of molecular orbitals as linear combinations of atomic orbitals (MO LCAO). The calculations are performed with the GAMESS program package (US). The correlation corrections are included in the calculations. The validity of the model parameters is verified by comparing the calculated with experimental structural and dynamic properties of ideal alkali halide crystals.     

Stationary inverted Lyman populations and free-free and bound-free emission of lower-energy state hydride ion formed by an exothermic catalytic reaction of atomic hydrogen and certain group I catalysts

Rb⁺ to Rb²⁺ and 2K⁺ to K + K²⁺ each provide a reaction with a net enthalpy equal to the potential energy of atomic hydrogen. The presence of these gaseous ions with thermally dissociated hydrogen formed a plasma having strong VUV emission with a stationary inverted Lyman population. Significant Balmer α line broadening of 18 and 9 eV was observed from a rt-plasma of hydrogen with KNO₃, and RbNO₃, respectively, compared to 3 eV from a hydrogen microwave plasma. The reaction was exothermic since excess power of about 20 mW/cc was measured by Calvet calorimetry. We propose an energetic catalytic reaction involving a resonance energy transfer between hydrogen atoms and Rb⁺ or 2K⁺ to form a very stable novel hydride ion. Its predicted binding energy of 3.0471 eV with the fine structure was observed at 4071 Å, and its predicted bound-free hyperfine structure lines matched those observed for about 40 lines to within.01 percent. Characteristic emission from each catalyst was observed. This catalytic reaction may pump a CW HI laser.     

Far-infrared absorption due to impurities in CsBr crystals

The far-infrared absorption in the phonon band of CsBr due to Na⁺, K⁺, Rb⁺, In⁺, and Tl⁺ impurities has been measured and compared with the calculated density of phonon states of the host lattice.     

离子与通道相互作用对NaK 通道通透特性影响的研究

以NaK 通道的三维精细结构为基础,从理论上阐述了NaK 通道对钠离子、钾离子、铷离子以及钙离子的通透机理,钡离子可以作为NaK 通道阻断剂的微观机理,我们的研究结果表明,通道与离子的相互作用是决定通道对不同离子选择性的基础, 反映通道与离子相互作用的位能曲线是通道对不同离子通透性的外在表现. 关键词： NaK 通道 密度泛函 布朗动力学 通透性     

Synthesis and Spectral Study of Several Solid M3[Eu(2,6-Pyridinedicarboxylate)3] Salts (M=Li+, Na+, K+, Rb+, Cs+, NH4 +, and Pyridinium+)

Abstract

Salts of the [Eu(2,6-pyridinedicarboxylate)₃]^3- complex anion and various monovalent inorganic and organic counterions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺, and pyridinium⁺) have been synthesized and studied by emission spectroscopy. The Eu³⁺ ion emission spectra exhibited by these salts have been observed with high resolution (less than 1.0 cm^?1) and at low temperature (77 K). The emission spectra of these compounds indicate that changing the attached counterion does not affect the site symmetry observed by the europium ion beyond slight distortions indicated by small shifts in the energies of the Eu³⁺ electronic levels.     

Improved luminescent properties of red-emitting Ca0.54Sr0.16Eu0.08Gd0.12(MoO4)0.2(WO4)0.8 phosphor for LED application by charge compensation

The red-emitting Ca_0.54Sr_0.16Eu_0.08Gd_0.12(MoO₄)_0.2(WO₄)_0.8 phosphor is improved in the emission charateristics by charge compensation, of which chromaticity coordinates (CIE) are x=0.66 and y=0.33. Three approaches to charge compensation are investigated, namely (a) 3Ca²⁺/Sr²⁺→2Eu³⁺/Gd³⁺+vacancy, (b) 2Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+M⁺(M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ employed as a charge compensator) and (c) Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+N⁻ (N⁻ is a monovalent anion like F⁻, Cl⁻, Br⁻ and I⁻ employed as charge compensation ions). Through photoluminescent spectra analyzing the radiative and non-radiative relaxation mechanisms of luminescent system are obtained. Under 20 mA forward-bias current, one red-emitting LED is made by combining 390-405 nm-emitting LED chip and the phosphor. The red-emitting phosphor has broad prospects in LED application field.     

Recombination luminescence of CaSO4:Tb3+ and CaSO4:Gd3+phosphors

A comparative study of the excitation of luminescence by VUV radiation as well as of thermally and photostimulated luminescence has been carried out for CaSO₄:Tb³⁺ and CaSO₄:Gd³⁺ phosphors, where Na⁺ or F⁻ ions are used for charge compensation. The distinction in hole processes for the phosphors with Na⁺ or F⁻ compensators is determined by the differing thermal stability of the holes localized at/near Tb³⁺Na⁺ and Gd³⁺Na⁺ (up to 100–160 K) or at/near Tb³⁺F⁻ V _Ca and Gd³⁺F⁻ V _Ca centers involving also a cation vacancy (up to 400–550 K). Tunnel luminescence in the pairs of localized electrons and holes nearby Tb³⁺ or Gd³⁺ has been detected. The mechanisms of electron-hole, hole-electron and tunnel recombination luminescence as well as a subsequent released energy transfer to RE³⁺ ions are considered.     

Influence of monovalent cationic impurities on plasticity of AgCl

The hardening effect of Li⁺, Na⁺, K⁺ and Rb⁺ impurities in polycrystalline AgCl was investigated. With increasing concentration of the impurities the flow stress increases and the plasticity decreases. By doping with a few ppm of Rb⁺ AgCl becomes very brittle. Comparing the results with the statistical theory of solid solution hardening, deviations were found.     

Electron Capture and Dissociative Excitation in Slow Collisions of Na+ and K+ Ions with Hydrogen and Nitrogen Molecules

Absolute cross sections of electron capture and dissociative excitation for the Na⁺-H₂, N₂ and K⁺-H₂, N₂ pairs are determined. The high intense hydrogen and nitrogen atomic lines HI (121.6 nm) NI (120.0 nm), have been observed. For the Na⁺-H₂ and K⁺-H₂ pairs the qualitative interpretation of experimental results in the framework of quasidiatomic approximation are carried out. This revised version was published online in July 2006 with corrections to the Cover Date.     

Compound synthesis in TiO2 implanted with Rubidium

Rubidium ions, with energy in the range 0.1 MeV, 2.0 MeV have been implanted in TiO₂ single crystals at RT and LNT.

Defects induced by implantation have been studied by optical spectroscopy, X-ray diffraction, RBS, TEM and electrical conductivity.

During implantation, the implanted samples are blue colored after irradiation. This coloration is due to an optical absorption band localized at 900 nm which corresponds to optical transition of intrinsic defects identified as Ti³⁺. These defects are induced by a chemical reaction between the implanted ions and the oxygen of the lattice as in the case of D⁺, H⁺, Li⁺, Na⁺ and K⁺ implanted in rutile.^1-3

The synthesis of a new phase in heavily implanted rutile is exhibited by using a thermal treatment and by combining techniques such as RBS, TEM and X-ray diffraction at glancing angle in the temperature range 300°C-700°C.

This compound does not correspond to metallic precipitates of rubidium which are observed in MgO implanted with Rb ions.

Planar defects have been observed in the implanted area. A correlation is exhibited between these defects and the precipitates of the new phase. From X-ray diffraction measurements and TEM observations, the composition of the synthetized compound is likely Rb₂TiO₃.     

Effects of alkali metal ions on upconversion photoluminescence intensity of Er3+-doped Y2O3 nanocrystals

We investigate upconversion emissions in alkali metal ions (Li⁺, Na⁺, and K⁺) and Er³⁺-codoped Y₂O₃ nanocrystals. By introducing Li⁺, upconversion intensity is significantly enhanced, while Na⁺ and K⁺ hardly have this influence. FT-IR data give evidence that the main mechanisms of the enhanced upconversion emission cannot be attributed to the decreased surface defects. EXAFS data and variations of enhanced upconversion intensities in different samples indicate that Li⁺ can occupy the interstitial sites in lattice and thus arouse large site asymmetry. In addition, locations in the samples and effects on the upconversion emission of Na⁺ and K⁺ are discussed.     

Electrical conductivity of superionic solid solutions of Na2SO4 with Mx (XO4)y -[M=Na,K, Rb,Cd, GdandX=W,Mo, S,Si;x=1, 2, 4 andy=1, 3]

Electrical conductivity data are reported for solid solutions of Na₂SO₄, K₂WO₄, Na₂WO₄, Na₂MoO₄, Rb₂SO₄, Na₄SiO₄ and Gd₂ (SO₄)₃. In all cases, except K₂SO₄, we observed an increase in Na⁺ conductivity effected by lattice expansion and/or incorporation of ion vacancies in addition to a structural transformation. Boundary conditions were shown to exist for these factors to yield a limiting Na⁺ conductivity with a constant fraction of Na⁺ based on a percolation model of transport. The higher conductivity data observed for the larger radius isovalent WO^2-₄ and aliovalent SiO^4-₄ doped Na₂SO₄ show conclusively that the anion-rotation ”cogwheel” mechanism does not contribute to the cationic conductivity in Na₂SO₄.     

Orientation and alignment generated from photoionization of closed-shell cations

The orientation parameter A₁₀ and the alignment parameter A₂₀ have been calculated for the single photoionization of the closed-shell cations Na⁺, Al⁺, K⁺, Cu⁺, Ga⁺, Rb⁺, Ag⁺, In⁺, Cs⁺, Au⁺, Tl⁺ and Fr⁺ where all possible vacancies from 2p_1/2 up to 6p_3/2 have been investigated. The calculations have been performed by employing a relaxed-orbital method within a single-configurational Hartree–Fock approach where mass–velocity and Darwin corrections have been incorporated into the non-relativistic approach. To cover the range of a possibly occurring Cooper minimum kinetic energies of the emitted photoelectron up to at least 20 Ry (≈ 272 eV) have been considered. The results are compared with the orientation and alignment parameters of the respective singly photoionized isoelectronic atoms to underline differences in the strength of repulsive barriers and in the energetic position of shape resonances and Cooper minima.     

Electrointercalation into 2H-TaS2 single crystals:in situ dilatometry and superconducting properties

Summary The electrointercalation of the following hydrated metal ions into 2H-TaS₂ crystals was investigated: Na⁺, K⁺, Ca²⁺, Zn²⁺, Mn²⁺, Co²⁺, La³⁺, Gd³⁺, Pr³⁺. We report onin situ dilatometric studies of the reaction and on superconducting properties of these compounds. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Electrical conductivity and dielectric loss in doped Pb(NO3)2 single crystals

dc ionic conductivity measurements were made on single crystals of Pb(NO₃)₂ doped with monovalent Na⁺ and K⁺ in the temperature range of 100–400°C. In the extrinsic region the conductivity was found to decrease with Na⁺ having a smaller ionic size, and to increase with K⁺ with larger ionic size compared to the host Pb ion. Conductivity is attributed to the mobility of anti-Frenkel defects as in the case of PbF₂. Dielectric loss measurements were made on the Pb(NO₃)₂: K⁺ system in the frequency range of 300 Hz to 20 kHz at different temperatures. Impurity vacancy pairs of the type K⁺-(NO^-₃)_V are found to be responsible for the observed dielectric loss peaks. The maximum peak frequency is found to increase with temperature.