Nonstoichiometric Salts Research Articles

On Diffusive Confining a Galvanic Crystallization out of Molten Salts

The electron-energy band structure of electric Double Layer (DL) between a molten salt and metal electrode (an anode or cathode) is studied for the electrodepositing crystallization process when the width of DL metal part is less than the one in the molten salt. It is shown that just the molten-salt part of the double layer confines a rate of electrodepositing process. The reason of this is a neutralization of depositing ions into the molten-salt near the electrode and hence their diffusively confined motion in a density gradient field. It is important to minimize the electrodepositing potential for effective component crystallization out of the molten salt and its exchange process including selective extracting of salt components by their crystallization on electrodes of galvanic circuit. It is shown that this can be carried out by means of fine and controllable variation of reduction-oxidation (RedOx) potential of the non-stoichiometric salts. A possible application of a potentiometer for monitoring and managing the salt composition is considered. For this, one uses precise methods of electric-motion-force and coulometer titration by solid electrolyte(for example, M+–β ”–Al2O3) of the basic salt metal (M。) as a reduction agent in the molten-salt solution.

A contribution to the physicochemical characterization of nonstoichiometric salts of tungstosilicic acid

Nonstoichiometric cesium and rubidium salts of tungstosilicic acid (TSA) were synthesized by precipitation. These solids are insoluble in water, due to the low solvation energy of large cations, have high specific surface area, and a mainly microporous structure. In turn, nonstoichiometric potassium salts prepared by solution evaporation have a low specific surface area and porosity, high solubility in water, and a negligible porosity. All the synthesized tungstosilicates presented a cubic structure, with a lattice parameter that slightly decreases in the order Cs + > Rb + ≅ K + salts. The salts displayed the characteristic FT-IR bands of TSA, though the band assigned to the stretching of the W O terminal bond presented a slight widening and a shoulder, and the band attributed to a bridged W O W bond was shifted to a lower wavenumber and showed a shoulder. Such effects are indicative of the interaction between the [SiW 12O 40] 4− anion and the alkaline cations. Assuming that an increase in 1H MAS-NMR chemical shift is due to a higher acid strength, the cesium salts would have acid sites with higher acid strength than the others. The potassium salts, however, presented protons in different acid environments, with a low proportion of very strong acid sites. The acidity measurement by potentiometric titration with n-butylamine also showed that the cesium salts have acid sites with higher strength than those of rubidium. The same behavior was observed for the potassium salts, which exhibited an acid strength higher than expected. The number of protons determined by titration decreased in the order Cs + > Rb + ≅ K + salts and also decreased for the more substituted salts.

Oxidation of TTF derivatives using (diacetoxyiodo)benzene: a general chemical route toward cation radicals, dications, and nonstoichiometric salts.

Oxidation of TTF derivatives using (diacetoxyiodo)benzene: a general chemical route toward cation radicals, dications, and nonstoichiometric salts.

Identification of trihalide anions in bis(ethylenedithio)tetrathiafulvalene salts by Raman spectroscopy

In order to distinguish individual contributions of trihalide anions in β-like structures of the (BEDT-TTF)2X organic conducting single crystals [where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X stands for I3, I–I–Br, Br–I–Br, Br–I–Cl, Cl–I–Cl or mixed trihalide anions], low frequency Raman spectra have been recorded at 25 K. This technique permitted us to establish a presence of a ternary mixture of I3, I–I–Br, and Br–I–Br anions in one of the nonstoichiometric salts and an existence of Br–I–Br, Br–I–Cl, and Cl–I–Cl anions in another one. It is not possible to detect these anions independently using the x-ray diffraction method. The ab initio calculated interatomic bond lengths and vibrational frequencies of trihalide anions are in good agreement with experimental data, which confirmed the assignment of observed low-frequency Raman bands. At 80 K the Raman spectra were taken for a fixed linear polarization of the incident laser light, and the examined single crystals were rotated in π/8 increments. In this way, an anisotropy of trihalide anion’s polarizability has been investigated to confirm the collinear arrangement of anions and the proposed assignment of Raman bands.

Metal−Oxygen Cluster Compounds (Heteropoly Oxometalates) of 1B and 3B Monovalent Cations and Their Micropore Structure

Silver and thallium, representatives from the periodic table's groups 1B and 3B, respectively, were employed as cations to synthesize stoichiometric and nonstoichiometric salts of 12-tungstophosphoric, 12-molybdophosphoric, and 12-tungstosilicic acids. All the solids, except silver 12-molybdophosphate, have high surface areas and microporous structures, as shown from the analysis of nitrogen adsorption−desorption isotherms obtained at 77 °K. Powder X-ray diffraction, temperature-programmed desorption, infrared spectroscopy, and 1H MAS NMR spectroscopy are employed to characterize the synthesized materials.

Ion-exchange properties of microporous monovalent salts of 12-tungstophosphoric acid and 12-molybdophosphoric acid catalysts

Ion exchange of the ammonium, potassium, and cesium salts of 12-tungstophosphoric and 12-molybdophosphoric acids has been studied at 298 K. Residual protons contained in the nonstoichiometric salts are exchanged as well as the original cations. The completeness of the ion-exchange process varied from approximately 5 to 70%, depending on both the solid phase and liquid phase cations. The maximum exchange capacities are shown to decrease significantly as the size of the cation leaving the solid becomes larger than that of the cation entering the solid.

The electrical and magnetic properties of TMDBFBF 4, ClO 4, AsF 6 and PF 6, the cation radical salts of tetramethoxydibenzofuran

The cation radical salts (crs) of tetramethoxydibenzofuran, (TMDBF)X, form non-stoichiometric salts with different anions (X = BF 4 −, ClO 4 −, AsF 6 − and PF 6 −). All investigated salts contained the solvent used in the electrocrystallization (CH 2Cl 2). The X-ray investigation showed that the crs were disordered. Conductivity measurements showed that the crs were thermally activated with Δ < 110 meV at high temperatures; at lower temperatures there are different deviations from this behaviour. All crs have σ rt ∼ 10 −2 (Ω cm) −1 . The susceptibilities are large, χ ∼ 10 −4 emu/mole, and barely temperature dependent between 300 and 50 K. Below 50 K, χ increases less than 1/ T. These results are interpreted using a common model for σ and χ. Due to the quasi one-dimensionality of the crs, the disorder present causes all states to be localized. This leads to charge transport by phonon-assisted hopping between localized states near the Fermi level, and a paramagnetic susceptibility due to antiferromagnetic order in one dimension. Interacting chain segments exist with weak exchanges ϵJ at a random concentration among uniform nearest-neighbour exchanges J. The narrow e.s.r. lines (about 100 mG at room temperature) are caused by exchange narrowing, with an exchange frequency of about 10 12 Hz.

Electrical, magnetic, and optical properties of the tetrathiafulvalene (TTF) pseudohalides,(TTF)12(SCN)7and(TTF)12(SeCN)7

The electrical, magnetic, and optical properties of charge-transfer salts containing tetrathiafulvalene (TTF) and the pseudohalides, thiocyanate (SCN) and selenocyanate (SeCN), have been investigated. These salts are quasi-one-dimensional compounds containing cation radicals only, in contrast to a cation-radical-anion-radical system, such as tetrathiafulvalene tetracyanoquinodimethane (TTF) (TCNQ). Measurements of electrical conductivity, thermoelectric power, and optical reflectivity of single crystals of the nonstoichiometric salts ${(\mathrm{TTF})}_{12}$${(\mathrm{SCN})}_{7}$ and ${(\mathrm{TTF})}_{12}$${(\mathrm{SeCN})}_{7}$ show metal-like characteristics above 200\ifmmode^\circ\else\textdegree\fi{}K (high-temperature region). The conductivities at room temperature are \ensuremath{\sim} 750 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$${\mathrm{cm}}^{\ensuremath{-}1}$, comparable to those found in (TTF) (TCNQ), and increase with decreasing temperature down to \ensuremath{\sim} 200\ifmmode^\circ\else\textdegree\fi{}K. The thermoelectric power at room temperature is small and positive (\ensuremath{\sim} 9 \ensuremath{\mu}V/\ifmmode^\circ\else\textdegree\fi{}K), and decreases linearly with decreasing temperature in this region (as expected for metal-like hole conduction along the TTF chains). The ESR intensity, however, decreases with decreasing temperature above 200\ifmmode^\circ\else\textdegree\fi{}K. At 170\ifmmode^\circ\else\textdegree\fi{}K a metal-nonmetal transition occurs, and the transport and magnetic properties below this temperature are characteristic of a semiconducting state.

Magnetic Analysis of the Uranium-Oxygen System

Magnetic susceptibility measurements have been carried out on the uranium-oxygen system in the composition range of U${\mathrm{O}}_{2}$ to U${\mathrm{O}}_{2.67}$. The existence of an antiferromagnetic transition at compositions close to stoichiometric U${\mathrm{O}}_{2}$ which had been previously reported by the authors has been confirmed. The data make it possible to define clearly the phase limits of the U${\mathrm{O}}_{2}$ and ${\mathrm{U}}_{3}$${\mathrm{O}}_{8}$ structures and to determine unambiguously that the excess oxygen ions in the nonstoichiometric salts occupy interstitial positions in the lattice.