Intercalation reaction of layered transition metal disulfides—II: Tetraalkylammonium hydroxide intercalates of 2H-tantalum and 2H-niobium disulfides

The intercalates of 2H-tantalum and 2H-niobium disulfides with tetraalkylammonium hydroxides were prepared in aqueous solutions. All intercalates prepared were hexagonal 2H-polytype, and their a-lattice parameters were similar to those of the original disulfides. The intercalates of both disulfides had similar c-lattice parameters, the values being 23Å in tetramethyl- and tetraethyl ammonium hydroxide intercalates, and 28Å in tetra-n-propyl- and tetra-n-butylammonium hydroxide intercalates, respectively. The increase in the c-lattice parameter was interpreted according to the effective ionic radii of tetraalkylammonium ions in aqueous solutions including alkali metal ions. It was found from this interpretation that the c-lattice parameter of the hydroxide intercalates increased stepwise at regular distances of 5Å corresponding to the increase in the effective ionic radius of the intercalated cations.     

Alkali metal intercalation into SnS2

The intercalation of sodium and potassium into the layered semiconductor SnS₂ has been investigated by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and ion scattering spectroscopy (ISS). After deposition of the alkali metals onto (0001) cleavage planes of SnS₂ in ultra high vacuum (UHV), semiconducting intercalation phases were formed. They seem to be homogeneous and disordered under the given experimental conditions. The valence electrons of the alkali metals are transferred into electronic states of the host lattice, whose valence band density of states changes significantly during intercalation. The underlying changes of the binding properties of the host lattice are discussed. The course of intercalation can be separated into three phases. During an induction period the concentration of the alkali metal on the surface remains very small, the electronic states of the substrate are shifted by band bending. During an intercalation period the topotactic reaction proceeds. After reaching saturation compositions of the intercalation phase at the surface, the alkali metal diffuses into the bulk. Crystal or surface defects seem to have a significant influence on the kinetics of intercalation and on the stoichiometry of the intercalation compounds.     

The electronic and magnetic properties of the 3d transition metal intercalates of TiS2

The introduction of 3d transition metals (M) into the van der Waals gaps between the weakly coupled layers of transition metal dichalcogenides TX₂ (T:transition metal, X:chalcogen) produces an interesting family of intercalation compounds, M _x TX₂, the physical properties of which are different from those of the host TX₂ matrix because of ‘host-guest’ interactions. In this article we shall review the salient features of the M _x TiS₂ family with the simple 1T-CdI₂ type layered structure, which have been extensively studied by structural, transport, specific heat and lattice dynamic, magnetic and photoemission spectroscopic measurements. In contrast with the previously reported series of intercalation complexes of the Group V transition metal dichalcogenides, a characteristic of the M _x TiS₂ materials is strong hybridisation between the guest atom M 3d orbitals and the host Ti 3d and S 3p orbitals, leading to changes in the Fermi energy E _F of the conduction band, the density of states at E _F and various types of magnetic orderings. These properties are understood in terms of an itinerant electron or band picture for the intercalant, rather than a rigid band or localised model.     

Ionic conductivity of alkali metal chloroaluminates

The electrical conductivity of three alkali metal chlorluminates has been investigated from room temperature to above the melting point. Ionic conductivities at 25°C are 1.2 × 10^?6, 3.5 × 10^?7 and 3.2 × 10^?9omh^?1 cm^?1, and activation enthalpies are 0.47, 0.46 and 0.53 eV for LiAlCl₄, NaAlCl₄ and KAlCl₄.     

Alkali metal intercalation in ternary and multinary compounds

Summary The group-IV,-V and-VI transition metal dichalcogenides are able to rapidly and reversibly incorporate significant concentrations of alkali metal ions (intercalants) within their layer structures. Because of their unusual combination of rapid mobility and high chemical stability for the intercalant, some of the alkali-metal-intercalated dichalcogenides are attractive candidates for high-energy battery electrodes. The structural characteristics of the lithium- and sodium-intercalated TiS₂ compounds, which are the most extensively investigated intercalated materials, are summarized. The chemical stability of intercalants is discussed, with an emphasis on the ternary-phase equilibria, electrochemicalcell voltage and intercalant interaction energies. Some recent investigations with multinary alkali metal intercalation compounds are then described. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

An alkali metal vapor laser amplifier

The operation of a transversely diode-pumped alkali metal vapor laser amplifier is theoretically studied. The amplifier operation is described by a rather intricate system of differential equations, which can be solved in the general case only numerically. In the case of intense incident radiation, an analytic solution is obtained which makes it possible to determine any energy characteristics of the laser amplifier and to find the optimal parameters of the active medium and pump radiation (temperature, buffer gas pressure, and intensity and width of the pump radiation spectrum).     

Dynamic holography in alkali metal vapour

Problems of dynamic hologram recording on resonant absorption lines of alkali metal vapour are discussed. Light beams and media parameters are determined that are necessary for hologram recording with usable efficiency. The effects of thermal atomic motion and the radiative transport of excitation influence on the spatial frequency transfer function of two-level media are investigated. Results of hologram recording in vapour of Rb (780.0 nm) and Cs (852.1 nm) using low-power CW-lasers are presented. Transmission holograms in the volume media and reflection holograms near the boundary of the resonant vapour and the dielectric are compared. For transmission holograms the advantage of collinear read-out when using pure vapour in comparison with a counterpropagating read-out is shown, and this makes it possible to achieve higher values of hologram efficiency over a wide range of atomic density. It is shown that reflection hologram recording is characterized by higher resolution, as compared with hologram recordings in the volume of extended media. Problems of metal vapour hologram usage for laser parameter control are discussed. The feasibility of holograms in Cs-vapour usage as a spectral-selective real-time feedback element in a semiconductor laser external cavity is shown.     

Supershell structure in alkali metal nanowires

Nanowires are formed by indenting and subsequently retracting two pieces of sodium metal. Their cross section gradually reduces upon retraction and the diameters can be obtained from the conductance. In previous work we have demonstrated that when one constructs a histogram of diameters from large numbers of indentation-retraction cycles such histograms show a periodic pattern of stable nanowire diameters due to shell structure in the conductance modes. Here, we report the observation of a modulation of this periodic pattern, in agreement with predictions of a supershell structure.     

Muon implantation in alkali metal hydrides

Zero, longitudinal and transverse field μSR measurements have been made on LiH, LiD and NaH. The primary motivation for the study was to elucidate the behaviour of the muons in the diamagnetic state and analysis of the time‐dependent zero field relaxation data suggests that negatively charged muonium, Mu^-, is formed and takes up a H^- vacancy site in these materials. Evidence is presented for a small (approximately 2%) reduction in the Mu^-–Li distance relative to the unperturbed nearest neighbour anion‐cation distances in the pure crystal lattices. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dissociation of doubly charged alkali metal clusters

We have studied the competition experimentally observed between fission and neutral atom evaporation, as dissociation channels of excited doubly charged sodium clusters, using the Density Functional Theory and the jellium model. The fission barrier has been obtained from an Extended Thomas-Fermi calculation including density gradient corrections to the kinetic energy of the electronic cloud. We discuss the influence of the coefficient of the density gradient term on the barrier height.     

Nonlinear electric properties of alkali metal halides

The first and second hyperpolarizabilities as well as the dipole moments and dipole polarizabilities are studied for a series of the alkali metal halides (MeX, Me = Li, Na, K, X = F, Cl, Br). The static results have been calculated at various levels of including the electron correlation contribution. The frequency-dependent data for different nonlinear optical processes correspond to TDHF calculations and can be approximately scaled for the electron correlation contribution. The present study also gives a systematic comparison of the performance of the so-called Pol basis sets and the recently developed basis sets (HyPol) designed for calculations of electric hyperpolarizabilities. Several regularities in the calculated data are observed and discussed in terms of ionic models supplemented by the electron density confinement effect. For some of the studied systems the first and second hyperpolarizabilities are found to have interestingly high values, comparable to those for molecules used in nonlinear optical materials.     

Conductivity of heavy alkali metal doped polyacetylene

The electrical conductivity, σ, of (MyCH)_x (M = K, Rb, Cs ; 0.08 < y ⩽.15) has been measured from 4.2 to 290 K on completely solvent free materials. The σ-T relationship is of the form σ = AT^α where 0.35 < α ⩽ 0.7 over most of the T range. The results are compared with other data concerning heavily-doped (CH)_x.     

The electronic structure of alkali metal oxides

Crystalline phase total energies, band structures, the distributions of the total and partial densities of electron states, and atomic charges were calculated for lithium, sodium, and potassium oxides, peroxides, superoxides, and ozonides using the CRYSTAL 06 and GAMESS packages in the B3LYP parameterization. For the molecular phases, the geometry was optimized and molecular orbital energies calculated. The results obtained for metal oxides were compared with the experimental photoelectron spectroscopy data and used to analyze their formation and thermal decomposition.     

Band structure and optical properties of alkali metal halides

Optical spectra, photoemission spectra, and photoconductivity spectra of alkali metal halides are analyzed using energy band structure calculations and selection rules for direct and indirect transitions. The main feature of the band structure of MeN₃ (Me: Na, K, Rb, Cs) as proposed by the authors is the presence of two conductivity bands, one anionic and the other cationic in nature. A weak dispersion of the valence subband indicates that phonons may yield a significant contribution to the observed spectra. All of the optical and photoemission spectra so far reported for the metal azides may be explained on the basis of the proposed band model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 3–7, January, 1995.     

Static polarizability of excited and charged alkali metal clusters

The static polarizability of the excited and positively charged (from 1 to 5) sodium, lithium, and potassium clusters containing the “magic” number of valence electrons (from 8 to 198) is calculated by the density-functional method within the “jellium” model. The dependences of the polarizability on the state, size, charge, and composition of clusters are analyzed.