Arrangement Of Cations Research Articles

Proton Conducting Ionic Liquid Doped Nafion Membranes: Nano-Structuration, Transport Properties and Water Sorption

The impact of triethylammmonium trifluorosulfonate (TFTEA) concentration on the nanostructuration and electrochemical, thermo mechanical, transport properties of doped Nafion membranes has been studied. The Nafion membranes neutralized with triethylamine (Nafion–TEA) have been doped with various amounts of TFTEA using the swelling method. The effect of the TEA neutralization was first studied. The results suggest a specific arrangement of TEA cations and a quite low water uptake. Concerning TFTEA doped membranes, the evolution trend of nanostructure of TFTEA doped Nafion is very similar to that of acidic Nafion swollen by water, with a slope equal to 1.33. However, at high TFTEA concentration (29 wt %) in this composite membrane, the average hydrophobic–hydrophilic phase separation distance appears to be 59 A while it is 41 A in hydrated acidic Nafion at the same volume fraction of polymer, which could be related to a much more heterogeneous distribution of TFTEA in Nafion–TEA than water molecules in acid...

Pressure-induced phase transitions and structure of chemically ordered nanoregions in the lead-free relaxor ferroelectric Na1/2Bi1/2TiO3

We investigate the phase stability of Na${}_{1/2}$Bi${}_{1/2}$TiO${}_{3}$, a prototype lead-free relaxor material, under pressure. By means of total energy calculations within density functional theory, we study the pressure stability of several structures with polar and antipolar distortions, in-phase and out-of-phase tilts, and different chemically ordered configurations. Under positive (compressive) pressure an orthorhombic $Pbnm$-like phase is stabilized above 3 GPa. At negative (tensile) pressure a non-tilted polar $P4mm$-like phase is stable. At zero pressure two phases are coexisting. The local chemical configuration determines whether the high-pressure $Pbnm$-like or another tilted and polar $R3c$-like structure is favored. Thus, two different variants of pressure phase diagrams depending on the cation arrangement are obtained, which raises the question of the existence of a mixed phase ground state in the disordered system. We discuss the stability of the mixed phase state in terms of lattice and tilt misfits and possible shapes and ferroic properties of the coexisting regions with different average structures. Our results clearly support the view that there are chemically ordered nanoregions with their own local ferroic properties embedded in a chemically disordered ferroelectric matrix representing the ground state.

Syntheses and molecular structures of four inorganic–organic hybrid compounds from N-containing aromatic bases and perchlorometallates of Zn, Cu, Sn, and Fe

Four organic–inorganic crystals, [(HL1)2(ZnCl4)]·H2O (1) (L1 = 2-methylquinoline), [(HL1)2(CuCl4)] (2), [(HL2)2SnCl6] (3) (L2 = 6-bromobenzo[d]thiazol-2-amine), and [(HL3)FeCl4] (4) (L3 = 5,7-dimethyl-1,8-naphthyridine-2-amine), derived from N-containing aromatic Brønsted bases and metal(II) chlorides (zinc(II) chloride, copper(II) chloride dihydrate, tin(II) chloride dihydrate, and iron(III) chloride hexahydrate) were prepared at room temperature and characterized by IR, X-ray structure analysis, elemental analysis, and TG analysis. The crystals are built up by perchlorometallates (Zn, Cu, Sn, and Fe) associated with organic cations through multiple non-covalent associations. X-ray diffraction analysis reveals that 1 and 2 have 3-D network structures built from hydrogen bonds between the cations and chlorometallates. Water molecules play an important role in structure extension in 1. Anhydrous 3 and 4 produced from 2-aminoheterocyclic derivatives display 2-D sheet structures. Arrangements of anions and cations are dominated by shape and size of cations, and also by the different structures of the chlorometallates as well as non-bonding interactions in the crystal structures. Except for 1, the other compounds are thermally stable below 240°C.

Short-range order in tourmaline: a vibrational spectroscopic approach to elbaite

Polarized Fourier-transform infrared and Raman spectra were acquired on an elbaite sample previously characterized by electron- and ion microprobe analysis, X-ray diffraction and structure refinement. Spectra from the two vibrational spectroscopy techniques reveal a close similarity in the OH-stretching region, with three main absorption bands strongly polarized in the c-axis direction. By means of bond-valence theory arguments, the observed OH bands are interpreted and assigned to specific local cation arrangements around the O1 (≡W) and O3 (≡V) anion sites. In combination with the relatively simple composition of the studied sample, bond-valence constraints are used to identify stable anion-cation arrangements, which permit the occurrence of short-range ordering to be assessed. Evidence for nearly complete short-range order at the O1 site, with the stable arrangements Y(LiAlAl)0.6–W(OH)0.6 and Y(LiLiAl)0.4–W(F)0.4, are presented. These two local arrangements can be further expanded to obtain the larger ordered clusters [W(OH)–Y(LiAl2)–V(OH)3–Z(Al)6]0.6 and [W(F)–Y(Li2Al)–V(OH)3–Z(Al)6]0.4.

X-ray diffraction study of the heterovalent copper compound [Cu4(OH)4 Bipy 4][Cu2(B10H10)3] · 4CH3CN

X-ray diffraction studies of three samples of the [Cu4(OH)4 Bipy 4][Cu2(B10H10)3]·4CH3CN crystals reveal a small amount (4–6%) of the second component, which is related to the main component by a mirror pseudoplane. An analysis of the geometric structure and mutual arrangement of complex cations [Cu4(OH)4 Bipy 4]4+ and anions [Cu2(B10H10)3]4− in the cell shows that replacing structural elements by their mirror equivalents results in insignificant steric conflicts. The existence of this minor crystal component can be attributed to point substitution defects or a separate twin individual.

Detailed insights into the structural properties and oxygen-pathways in orthorhombic Ba0.5Sr0.5Co0.8Fe0.2O3–δ by electronic-structure theory

A number of structural properties of orthorhombic Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) have been investigated by means of quantum-chemical calculations based on density-functional theory (DFT) and compared with experimental results. The role of the cation arrangements and the location of the oxygen vacancies within the orthorhombic structure have been evaluated and explained by means of bond-analytical techniques. Moreover, a detailed investigation of all oxygen pathways within orthorhombic BSCF has been performed, and the calculations show the existence of preferred oxygen pathways.

First-principles calculation of magnetoelastic coefficients and magnetostriction in the spinel ferrites CoFe2O4and NiFe2O4

We present calculations of magnetostriction constants for the spinel ferrites CoFe2O4 and NiFe2O4 using density functional theory within the GGA+U approach. Special emphasis is devoted to the influence of different possible cation distributions on the B site sublattice of the inverse spinel structure on the calculated elastic and magnetoelastic constants. We show that the resulting symmetry-lowering has only a negligible effect on the elastic constants of both systems as well as on the magnetoelastic response of NiFe2O4, whereas the magnetoelastic response of CoFe2O4 depends more strongly on the specific cation arrangement. In all cases our calculated magnetostriction constants are in good agreement with available experimental data. Our work thus paves the way for more detailed first-principles studies regarding the effect of stoichiometry and cation inversion on the magnetostrictive properties of spinel ferrites.

Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolution

Nano-particulate Co doped ruthenium dioxide electrocatalysts of the general formula Ru1−xCoxO2−y (0<x 0.3) were prepared by a co-precipitation method. The electrocatalysts with x<0.2 conform to a single phase nano-crystalline materials. On the local level the Co forms clusters dispersed in the original rutile-like matrix. The local environment of the Co conforms to a rutile model which preserves the cationic arrangement but suppresses the probability of the Ru–Ru and Co–Co neighbors along the shortest metal–metal bonds. The electrocatalytic activity of the synthesized Ru1−xCoxO2-y materials in oxygen evolution is comparable with that of the non-doped ruthenium dioxide and little depends on the actual Co content. In presence of chlorides the Co doped materials are more selective towards oxygen evolution compared with the non doped ruthenia. The enhanced oxygen evolution in the case of Co doped electrocatalysts can be attributed to a chemical recombination of surface confined oxo-species. The selectivity shift towards oxygen evolution can be linked with limited activity of the Ru1−xCoxO2-y materials in the chlorine evolution reaction which seems to be relatively weakly dependent on the chloride concentration.

Preparation and characterization of spermine-exchanged montmorillonite and interaction with the herbicide fluometuron

We studied the interaction between the naturally occurring polycation spermine (SPERM) and Na-exchanged SWy-2 Wyoming montmorillonite (Na-SWy-2 Mt) and between spermine-exchanged montmorillonite (Mt-SPERM) and the herbicide fluometuron. Mt-SPERM with spermine contents ranging between 0 and 1.2 times the cation exchange capacity (CEC) of Na-SWy-2 were studied by XRD, FTIR and TGA analysis. Spermine was intercalated stoichiometrically into Na-SWy-2 up to the CEC of the clay mineral, resulting in basal spacing of 1.29nm. TGA analysis indicated that intercalation of spermine into Na-SWy-2 increased the thermal stability of the organic cations and affected the dehydroxylation temperature of the clay mineral. FTIR measurements of Mt-SPERM samples showed the involvement of NH and CH groups of spermine in the interaction with the clay mineral. The intensity of the spermine NH and CH deformation vibrations increased linearly with the amount of spermine incorporated into Na-SWy-2 up to an amount close to the CEC of the montmorillonite. Structural modeling suggested that the arrangement of spermine cations formed a horizontal monolayer within the interlayer space of SWy-2 with strong interaction between the NH3+ and NH2+-groups of spermine and the montmorillonite surface oxygen atoms. Mt-SPERM showed pronounced affinity for the herbicide fluometuron.

Structural and electronic properties of the LiNiPO4 orthophosphate

Microcrystalline LiNiPO4 powders have been prepared by solid-state reaction using various precursors. Characterization of the structure and morphology of powders was performed using XRD, SEM, HRTEM, Raman, and FTIR. The electronic properties of materials were investigated by SQUID and ESR. The LiNiPO4 material adopts the olivine-like structure (Pnma S.G.). Analysis of the Raman and FTIR spectra figures out, with the aid of a molecular vibration model, the bonding between NiO6 octahedral and (PO4)3− tetrahedral groups. The electronic configuration and the local cationic arrangement are confirmed by magnetic susceptibility and electron spin resonance spectroscopy.

Triangular Nickel Complexes Derived from 2-Pyridylcyanoxime: An Approach to the Magnetic Properties of the [Ni3(μ3-OH){pyC(R)NO}3]2+ Core

A series of nickel complexes with nuclearity ranging from Ni(3) to Ni(6) have been obtained by treatment of a variety of nickel salts with the 2-pyridylcyanoxime ligand. The reported compounds have as a common structural feature the triangular arrangement of nickel cations bridged by a central μ(3)-oxo/alkoxo ligand. These compounds are simultaneously the first nickel derivatives of the 2-pyridylcyanoxime ligand and the first examples of isolated, μ(3)-O triangular pyridyloximate nickel complexes. Magnetic measurements reveal antiferromagnetic interactions promoted by the μ(3)-O and oximato superexchange pathways and comparison of the experimental structural and magnetic data with DFT calculations give an in-depth explanation of the factors that determine the magnetic interaction in this kind of system.

Comparative X-ray diffraction and infrared spectroscopy study of Zn–Al layered double hydroxides: Vanadate vs nitrate

Zn–Al layered double hydroxides (LDH) are promising as nanocontainers of corrosion inhibitors in self-healing corrosion protection coatings. Zn(2)Al–vanadate (Zn/Al=2:1) is prepared by anion exchange from the parent composition Zn(2)Al–nitrate at pH∼8. Crystal structure and vibrational spectra of both LDHs have been studied in comparison. Their interlayer distances are rather larger than those corresponding to the most compact arrangement of the intercalated anions. Nevertheless, no sign of a turbostratic disorder has been detected in these LDH. Based on the analysis of the spectroscopic data in combination with the XRD results, it has been shown that vanadate anion, which substitutes nitrate at the anion exchange, is pyrovanadate, V2O74-. The observed disorder in the hydroxide layers in Zn(2)Al–V2O7 is likely to result from strong interactions between V5+ and Zn2+/Al3. Although Zn(2)Al–NO3 is less disordered than Zn(2)Al–V2O7, it exhibits no long-range order in arrangement of cations in the hydroxide layers.

Two succinic acid derivatives of 2-ethyl-6-methylpyridin-3-ol

Crystals of bis(2-ethyl-3-hydroxy-6-methylpyridinium) succinate-succinic acid (1/1), C(8)H(12)NO(+)·0.5C(4)H(4)O(4)(2-)·0.5C(4)H(6)O(4), (I), and 2-ethyl-3-hydroxy-6-methylpyridinium hydrogen succinate, C(8)H(12)NO(+)·C(4)H(5)O(4)(-), (II), were obtained by reaction of 2-ethyl-6-methylpyridin-3-ol with succinic acid. The succinate anion and succinic acid molecule in (I) are located about centres of inversion. Intermolecular O-H···O, N-H···O and C-H···O hydrogen bonds are responsible for the formation of a three-dimensional network in the crystal structure of (I) and a two-dimensional network in the crystal structure of (II). Both structures are additionally stabilized by π-π interactions between symmetry-related pyridine rings, forming a rod-like cationic arrangement for (I) and cationic dimers for (II).

Structures of the strontium and barium dodecahydro- closo-dodecaborates

The structures of the anhydrous alkaline-earth-metal dodecahydro- closo-dodecaborates, SrB 12H 12 and BaB 12H 12, were determined by X-ray and neutron powder diffraction methods corroborated by a combination of neutron vibrational spectroscopic data and density-functional-theory-based phonon calculations. Both compounds possess the same novel trigonal structure with P31 c space group symmetry, which appears to represent the most stable arrangement of alkaline-earth cations and dodecahydro- closo-dodecaborate anions for cations above a certain size.

Mixing Thermodynamics of the Calcite-Structured (Mn,Ca)CO3 Solid Solution: A Computer Simulation Study

We have employed atomistic simulation techniques to investigate the thermodynamics of mixing in the solid solutions of calcite (CaCO(3)) and rhodochrosite (MnCO(3)). Our calculations show that the fully disordered solid solution has positive enthalpies of mixing for the entire range of compositions, which confirm recent experiments. The consideration of a small degree of ordering in the simulations leads to mixing enthalpies in quantitative agreement with experimental measurements. We argue that earlier measurements of negative mixing enthalpies for the Mn-rich solid solution were probably due to relatively high degrees of ordering in the samples. Our calculations show that the lowest energy configuration for each composition is always the one that maximizes the homogeneity of the cations within (0001) layers but maximizes the heterogeneity across layers. In particular, for Mn/Ca = 1, the most stable configuration corresponds to the ordered structure of kutnahorite, where layers of Ca and Mn ions alternate along the c axis, similar to the Ca/Mg ordering in dolomite. Our simulations predict that kutnahorite becomes less stable than the fully disordered 50:50 solid solution at ~850 K, and this disordering temperature decreases to a value in better agreement with experiment (695 K), if a transition to a partially ordered structure is considered. Our results thus suggest that the "disordered" (Mn,Ca)CO(3) solid solutions, which are known to be favored by kinetic factors, are actually not fully disordered, but contain a higher abundance of lower-energy cation arrangements than that expected from a completely random distribution.

와이오밍 벤토나이트의 유변학적 특성: 염분농도의 역할

팽윤성 점토의 전단강도 및 유변학적 특성은 점토입자의 크기, 양이온 교환능력, 점토광물학적 조성과 형상 등에 영향을 받는다. 본 연구는 고운 분말가루의 와이오밍(Wyoming) 벤토나이트에 대해 염화나트륨 0g/L 와 30g/L 농도로 24시간 수화시킨 후 염분농도에 따른 물성-강도특성 및 유변학적 특성변화를 살펴봄으로써, 유변학적 특성, 유변화적 모델들의 적용성 및 흙 입자의 구조변화에 따른 항복응력-점도와의 상관관계를 설명하고자 한다. 실험결과에 따르면, 팽윤성 점토는 전단담화(shear thinning)와 항복응력과 소성점도로 표현가능한 Bingham 유체 거동을 보이는 것으로 조사되었다. 염분농도가 낮고 함수비가 높아질수록 벤토나이트는 완전소성거동에 가깝게 나타나며, 전단변형률속도에 따른 변화의 폭이 미미한 것으로 조사되었다. 반면, 염분농도가 높아질수록 전형적인 전단담화거동을 보이며, 전단변형률속도를 증가시킬수록 염분농도에 따른 벤토나이트의 전단강도의 차이는 커진다. S=0g/L에 대해 Carreau, Herschel-Bulkley 및 멱수법칙 모델이, S=30g/L에 대해서는 이중선형, Herschel-Bulkley 및 멱수법칙 모델 등이 흐름특성을 가장 잘 표현한다. 이것은 염분농도에 따른 흙 입자간 구조적 배열과 형상이 입자간 발생하는 인력인 능-능(EE), 능-면(EF), 및 면-면(FF) 구조를 변화시키고 역학적 특성에 영향을 미치기 때문이다. The rheological properties of Wyoming bentonites are strongly influenced by the size of particles, cation exchangeable capacity, arrangement and morphology of clay mineral. This paper presents the results of rheological investigations on the Wyoming bentonites aqueous dispersions: two types of particle flocculation were considered. For the Wyoming bentonite, 0g/L and 30g/L NaCl equivalent salinity were added in fresh and salt water to examine the rheological behavior. This paper examined the general rheological characteristics, compatibility of rheological models and correlation between soil structure and change in rheological properties of Wyoming bentonite caused by increasing salinity. From flow curves of bentonites hydrated with fresh water and salt water, the observed general flow behavior is very close to shear thinning with yield stress (or ideal Bingham fluid with yield stress and plastic viscosity). However, the change of shear stress at the same shear rate is clear, particularly for lower shear rate. Well-known rheological models are used to fit the data. There is a good agreement between rheological model and data: Carreau, Herschel-Bulkley and power-law for S=0g/L and bilinear, Herschel-Bulkley and power-law for S=30g/L. It may be due to the fact that the internal structural bonding (strong modification of particle-particle interactions from edge-to-edge and/or edge-to-face to face-to-face) in soil matrix is affected from the evolution of rheological properties with different salinities.

Understanding 6Li MAS NMR spectra of Li2MSiO4 materials (M=Mn, Fe, Zn)

Analysis of 6Li MAS NMR spectra of several lithium transition-metal orthosilicates (Li2MSiO4, M=Mn, Fe, Zn) improved the understanding of the relation between the spectral parameters and the structural characteristics of the materials. It was shown that for manganese- and iron-containing materials the width of the 6Li spinning-sideband powder patterns can be roughly related to the arrangement of the transition-metal cations within the first cation coordination sphere around lithium. In mixed zinc–manganese lithium orthosilicates the 6Li isotropic shift depends on the number of Li–O–Mn bonds, in which a particular lithium site is involved. Each bond contributes a small negative Fermi-contact hyperfine shift of about −20 to −40ppm. The precise values of the contributions cannot be easily related to the geometry of the bonds. In iron-containing materials the isotropic shifts are composed of two contributions, the hyperfine shift and the pseudo-contact shift. The latter depends on the anisotropy of the magnetic susceptibility of the material. The magnetic properties of the iron-containing lithium orthosilicates are responsible also for very broad lines within their 6Li MAS NMR spectra. Pure zinc-lithium orthosilicate exhibits a narrow 6Li MAS NMR isotropic signal and no spinning-sideband powder pattern.

Computational study of the energetics of charge and cation mixing in U1−xCexO2

The formalism of electronic density-functional theory (DFT), with Hubbard-U corrections ($\text{DFT}+U$), is employed in a computational study of the energetics of fluorite-structured U${}_{1\ensuremath{-}x}$Ce${}_{x}$O${}_{2}$ mixtures. The computational approach makes use of a procedure which facilitates convergence of the calculations to multiple self-consistent $\text{DFT}+U$ solutions for a given cation arrangement, corresponding to different charge states for the U and Ce ions in several prototypical cation arrangements. Results indicate a significant dependence of the structural and energetic properties on the nature of both charge and cation ordering. With the effective Hubbard-U parameters that reproduce well the measured oxidation-reduction energies for urania and ceria, we find that charge transfer between U${}^{4+}$ and Ce${}^{4+}$ ions, leading to the formation of U${}^{5+}$ and Ce${}^{3+}$, gives rise to an increase in the mixing energy in the range of 4--14 kJ/mol of the formula unit, depending on the nature of the cation ordering. The results suggest that although charge transfer between uranium and cerium ions is disfavored energetically, it is likely to be entropically stabilized at the high temperatures relevant to the processing and service of urania-based solid solutions.

Effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4: A density functional theory study

The effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4 is investigated by GGA+U total energy calculations. We obtain a very strong (moderate) tendency for cation inversion in NiFe2O4 (CoFe2O4), in agreement with experimental bulk studies. This preference for the inverse spinel structure is reduced by tensile epitaxial strain, which can lead to strong sensitivity of the cation distribution on specific growth conditions in thin films. Furthermore, we obtain significant energy differences between different cation arrangements with the same degree of inversion, providing further evidence for recently proposed short range B site order in NiFe2O4.

Structural and magnetic properties of Nd 18Li 8Co 4− xFe xO 39− y and Nd 18Li 8Co 4− xTi xO 39− y

Nd 18Li 8Co 3FeO 39− y , Nd 18Li 8CoFe 3O 39− y and Nd 18Li 8Co 3TiO 39− y have been synthesised and characterised by neutron powder diffraction, magnetometry and Mössbauer spectroscopy. Their cubic structure ( Pm3̄ n, a∼11.9 Å) is based on intersecting <1 1 1> chains comprised of alternating octahedral and trigonal-prismatic coordination sites. These chains lie within hexagonal-prismatic cavities formed by a Nd–O framework. Each compound has an incomplete oxide sublattice ( y∼1), with vacancies located around the octahedral sites that lie at the points of chain intersection. These sites are fully occupied by a disordered arrangement of transition-metal cations but only 75% of the remaining octahedral sites are occupied. The trigonal-prismatic sites are fully occupied by lithium except in the case of Nd 18Li 8CoFe 3O 39− y where some iron is present. Antiferromagnetic interactions are present on the Nd sublattice in each composition, but a spin glass forms below 5 K when a high concentration of spins is also present on the octahedral sites.