Typical Ionic Compounds Research Articles

Unique switching mode of HfO2 among fluorite-type ferroelectric candidates

The primary uniqueness of HfO2 is its indispensible covalent bonding nature, though its high cation coordination number reflects a typical ionic compound.

The mechanical and thermal properties of natural rubber/zinc methacrylate composites by latex compounding techniques

AbstractZinc methacrylate (ZDMA) is a typical ionic compound that readily reacts with rubber molecules. In this work, a new approach was developed to prepare natural rubber (NR)/ZDMA composites with a lower loading of ZDMA. ZDMA was prepared by the reaction of methacrylic acid (MAA) and ZnO in an aqueous solution. Then the NR/ZDMA masterbatches were obtained by latex compounding techniques; followed by vulcanization either with dicumyl peroxide (DCP) or together with a sulfur‐based vulcanization system (SVS). The results of mechanical property tests showed that the increment of ZDMA will decrease the cure rate index and increase crosslink density. When the content of ZDMA was more than 8.7 phr, not only the 300% and 500% modulus, tensile, and tear strength of NR/ZDMA composites were improved remarkably, but also the aging resistance and thermal stability were improved. When the amount of ZDMA is less than 8.7 phr, SVS shows a certain synergistic vulcanization effect with DCP. When 20 phr ZDMA was added, the tensile and tear strength increased by 86.5% and 60.1%, respectively, when contrasted to NR cured with traditional SVS. The structural characterization results revealed that ZDMA and Poly‐ZDMA have been formed and act as a reactive filler in the NR matrix.

Theoretical exploration of the structural evolution of sodium sulfide clusters in Na-S batteries

The nanosized sodium sulfide species greatly enhance the performance of Na-S batteries. However, as a typical ionic compound, the diminished stability with decreasing cluster size has been rarely considered. Numerous theoretical works only simulated the Na-S binary system based on quite small sodium sulfide clusters, with no account of the stability of the sub-nanoscale cluster. Here, by using an advanced structure search algorithm, we built a binary phase diagram of the sodium sulfide clusters (NSCs). The commonly studied monomer model with low sulfur concentrations is indeed energetically unfavorable, especially for the final discharge product, the Na2S monomer. Therefore, the aggregation of monomers should take place to form multimers. According to the energy, charge, and geometry, relatively stable clusters with low sulfur concentrations are located, including (Na2S5)2, (Na2S4)2, (Na2S3)3, (Na2S2)4, and (Na2S)6 clusters. Furthermore, these multimers bind more intensely to four typical models of carbon-based substrates. The B-doped carbon material exhibits outstanding affinity to NSCs, which may facilitate overcoming the shuttle effect in applications. This work represents a significant step toward understanding the evolution mechanism of NSCs that may guide the future development of high-performance Na-S batteries.

Theoretical study on the hydrogen storage properties of (MgO)<sub>4</sub> under external electric field

MgO is a typical ionic compound with strong polarity. Hydrogen absorbed by MgO materials subjected to an external electric field is a potential method to store hydrogen. However, the method requires an extremely high intensity of electric field, which is difficult to achieve. Therefore, reducing field intensity has become a key problem in the field of hydrogen storage. In this paper, the hydrogen storage properties of an (MgO)<sub>4</sub> cluster under an external electric field are investigated. The results show that under the external electric field, (MgO)<sub>4</sub> keeps the frame of cube structure but with little distortion, which implies that (MgO)<sub>4</sub> cluster can sustain the strong electric field. The (MgO)<sub>4</sub> is also polarized by the external electric field and its dipole momentum increases to 1.67 and 3.33 Debye when the field intensity is 0.005 and 0.010 a.u., respectively. H<sub>2</sub> can be adsorbed on a single Mg/O atom: H<sub>2</sub> is adsorbed at lateral position of Mg atom, while at the top of O atom. The adsorption strength is substantially enhanced under an external electric field. Under only 0.010 a. u. of electric field, the adsorption energy of H<sub>2</sub> on the Mg or O atoms increases from –0.118 eV to –0.225 eV or from –0.060 eV to –0.150 eV, respectively. The electric field required is significantly lower than that of a large (MgO)<sub>9</sub> cluster. This result suggests that reducing the size of material is a possible method toreduce the electric field for hydrogen storage in polarizable materials. The weak interaction between H<sub>2</sub> and (MgO)<sub>4</sub> is analyzed by the quantum theory of atoms in molecules. The results indicate that under an electric field, (MgO)<sub>4</sub> and H<sub>2</sub> are effectively polarized, and the electrostatic interaction between them is subsequently enhanced. Meanwhile, the small cluster is easily polarized because most of the atoms are in the surface and have low coordination. Therefore, the electric field required can be substantially reduced. Moreover, (MgO)<sub>4</sub> adsorbs 16 H<sub>2</sub> molecules at most. The corresponding mass density of hydrogen storage reaches 16.7 wt%, indicating that (MgO)<sub>4</sub> can be used as a hydrogen storage material under an electric field.

Scientific Approach for a Cleaner Environment Using Ionic Liquids

Ionic liquids (ILs) are ionic compounds composed of a bulky organic cation and a smaller anion. The size mismatch leads to the low melting points relative to typical ionic compounds such as NaCl. ILs have become a very fruitful area of academic and industrial research primarily because of their beneficial and diverse properties. Ionic liquids characteristically have low vapor pressures, good solvency, high ionic conductivities, and good heat transfer properties. Our work on different combinations of cations and anions has led to a wide span of properties, such as acidity, water solubility, chemical reactivity, viscosity, melting points, etc. Further optimization of a property for a particular application was accomplished through synthesis and compositional variations. Ionic liquid compositions can be tailored to make them much greener than many traditional solvents and catalysts. Volatile organic compounds (VOCs) may cause air pollution and health issues. As a result industrial processes are looking for s...

Ionic compound mediated rearrangement of 3, 4, 9, 10-perylene tetracarboxylic dianhydride molecules on Ag(100) surface

Tailoring of the assembly structure of organic molecular monolayer is of great importance to improve the performance of molecular devices. In this work, a typical ionic compound, namely KCl, was used to mediate the rearrangement of 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA) monolayer on Ag(100). Combined scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) results indicate that both molecule and molecular superlattice would rotate after the dosing of KCl. The density functional theory calculation shows that KCl would exist in the form of molecules rather than ions on Ag(100) and demonstrates that experimentally observed structural transition induced by KCl molecules is energetically favored.

Formation of Stoichiometric CsFn Compounds

Alkali halides MX, have been viewed as typical ionic compounds, characterized by 1:1 ratio necessary for charge balance between M+ and X−. It was proposed that group I elements like Cs can be oxidized further under high pressure. Here we perform a comprehensive study for the CsF-F system at pressures up to 100 GPa, and find extremely versatile chemistry. A series of CsFn (n ≥ 1) compounds are predicted to be stable already at ambient pressure. Under pressure, 5p electrons of Cs atoms become active, with growing tendency to form Cs (III) and (V) valence states at fluorine-rich conditions. Although Cs (II) and (IV) are not energetically favoured, the interplay between two mechanisms (polyfluoride anions and polyvalent Cs cations) allows CsF2 and CsF4 compounds to be stable under pressure. The estimated defluorination temperatures of CsFn (n = 2,3,5) compounds at atmospheric pressure (218°C, 150°C, -15°C, respectively), are attractive for fluorine storage applications.

A Novel Cyanide-Free Gold Complex: [Au(tu)<sub>2</sub> ]SCN H<sub>2</sub>O

A novel aurous complex containing thiourea and thiocyanate as the mixed ligands is synthesized by the ISRC method in this paper. Its formula is determined as [Au (tu)2 ]SCN H2O by elemental analysis. The electrochemistry studies show it is a typical ionic compound and its conductivity reaches 13×10-4 Sm2mol-1. TG studies and related stability tests reveal the compound is excellently stable. By using single factors experiments the optimal plating index has been gotten and they are: pH=1.5~3.5, [A =1.5~2.5 g/L, temperature 30~50°C and plating time 10 minutes respectively. It is a competitive gold complex and will be find a wide application in electroplating, chemical deposition, ceramic decoration and other related areas.

Li 3 – O – Li 3 molecule: A metal-nonmetal-metal sandwichlike compound with a distending electron cloud

The D3d and D2d isomers of the Li3-O-Li3 molecule are metal-nonmetal-metal sandwichlike structures that contain two Li3 superalkali atoms. Their geometries and the real frequencies are obtained at the CCSD(T)/aug-cc-pVDZ level. They are different from the traditional types of the nonmetal-metal-nonmetal sandwich compounds. The natural bond orbital calculation and the topological property nabla2rho(r) calculation indicate that they are typical ionic compounds. In two isomers, the O2- anion is sandwiched in between two Li3+ cation rings. However, the different orientations of two Li3+ planes give the D3d isomer its own special characteristics. Under the action of the O2- anion in the center, the valence electrons of the D3d isomer are pushed out from two Li3+ triangle rings. This special interaction causes three phenomena. First, the valence electron clouds are distended. Second, the vertical ionization energy of the D3d isomer is considerably low, 4.39 eV, so that it may also be viewed as a superalkali atom. Third, we find that the D3d isomer owns the out-of-plane aromaticity and the largest negative nucleus-independent chemical shift value (-10.8 ppm) exists at 2.5 A above the center of the Li3+ ring, not at the center of the Li3+ ring like the isolated aromatic Li3+ cation.

XANES spectra of sesqui-oxides of Al, Cr and Fe

Abstract Oxygen X-ray absorption near edge (XANES) spectra obtained from α-Al 2 O 3 , Cr 2 O 3 and α-Fe 2 O 3 were found to be clearly distinguishable. The energy distributions of the XANES spectra were reproduced here fairly well by the DV-Xα molecular orbital calculation. On the other hand, O Kα spectra emitted from these oxides showed no significant difference. This indicates that the XANES is a very promising candidate to study the chemical environment of anions in typical ionic compounds.

Semi-Ionic Type Bonds in Fluorinated Carbon Compounds

Fluorinated graphite oxides (FGO) and fluorinated lignin (FL) have been investigated by X-ray photoelectron spectroscopy (XPS). In the F1s spectra of both compounds a peak with the energy being intermediate between the value in a typical ionic compound LiF and covalent compounds of type (CF)n and-(CF2-CF2)n- was extracted. The substances under study, even at high oxidizer content, contain structure fragments with carbon having sp2-hybridized orbitals. The bond formed between fluorine and these fragments is of semi-ionic type. The temperature, which allows the semi-ionic fluorine-carbon bond formation, is found to be between the room temperature and 100°C. The registration of semi-ionic state of fluorine in the FL allows to assume that the layered structure of initial substance is not necessary for the formation of semi-ionic bond between fluorine and carbon.

Analysis of thermally stimulated currents measured on ionic conductors

We propose a new method for analyzing the experimental results obtained from thermally stimulated depolarization current experiments on ionic conductors. This method is based on a model developed to explain polarization in these materials. The fundamental assumptions about the elementary mechanisms responsible for polarization is assumed to be due to the “free” volume created by thermal fluctuations occurring in solids near the equilibrium state. The consequence of these fluctuations is a statistical distribution of the relaxation times or energies, which can be evidenced by the thermal windowing technique, and then analyzed by relaxation map analysis. Applied to two typical ionic compounds, the method described in this work allows us to determine more realistic values of energy and τ0, corresponding to the measured relaxation times.

X-ray photoelectron spectroscopic study of montmorillonite containing exchangeable divalent cations

Montmorillonite containing divalent Mg, Ca, Sr, Ba or Cd as an exchangeable cation has been studied by X-ray photoelectron spectroscopy and X-ray-induced Auger electron spectroscopy. The relative atomic abundances of the exchangeable cations in the montmorillonite samples, obtained by X.p.s. measurements, are consistent with the cation-exchange capacity of the montmorillonite. A comparison of the photoelectron binding energies and Auger electron kinetic energies of the exchangeable cations with those of corresponding halides and oxides reveals that they fall among those of corresponding cations in typical ionic compounds such as fluorides and chlorides. On the other hand, the bonding state of the non-exchangeable Mg ion in montmorillonite lattice, as indicated by the Mg ls and KL2, 3L2, 3 Auger electron energies, is similar to that of magnesium oxide and distinguishable from that of the exchangeable Mg ion.