Anion Ordering Research Articles

Study of Anion Order/Disorder in RTaN2O (R = La, Ce, Pr) Perovskite Nitride Oxides

Symmetries and model structures are given for ABN2O (and ABNO2) perovskites that possess long-range ordering of anions in combination with a0a0c–, a–b0a–, and a–b+a– octahedral tilting. The stabilities of competing structures have been evaluated using density functional theory (DFT) calculations, which show that cis-ordered models are more stable than competing trans-ordered polymorphs. To test the validity of these predictions, the perovskite nitride oxides LaTaN2O, CeTaN2O, and PrTaN2O have been synthesized and characterized using neutron powder diffraction. CeTaN2O and PrTaN2O crystallize with orthorhombic Pnma symmetry (Ce: a = 5.69666(8), b = 8.03272(9), and c = 5.70893(7) A; Pr: a = 5.6868(1), b = 8.0153(1), and c = 5.68057(8) A) as a result of a–b+a– tilting of the octahedra. The structure of LaTaN2O is re-examined and found to possess orthorhombic Imma symmetry (a = 5.7093(1), b = 8.0591(2), and c = 5.7386(2) A) as a result of a–b0a– tilting. No evidence for long-range anion order is found in any ...

Principles and Applications of Anion Order in Solid Oxynitrides

Metal oxynitrides are emerging materials that may combine the advantages of oxides and nitrides. Anion order is important for controlling and tuning properties, and neutron diffraction provides good O/N contrast for experimental determinations of local or long-range O/N order in solids. Differences between oxide and nitride in charge, size, and covalent bonding are the important factors that drive anion order. An important example is the robust partial anion order in SrMO2N (M = Nb, Ta) and related oxynitride perovskites driven by covalency that results in disordered zigzag MN chains which segregate into planes within the perovskite lattice. This leads to unusual subextensive scaling of entropy, described as “open order”. Local anion order is important to optical materials. Size mismatch between host and dopant cations leads to local O/N clustering that tunes photoluminescence shifts systematically in M1.95Eu0.05Si5–xAlxN8–xOx phosphors, leading to a red shift when the M = Ba and Sr host cations are larger than the Eu2+ dopant but a blue shift when the M = Ca host is smaller.

Weathering and anthropogenic influences on the water and sediment chemistry of Wular Lake, Kashmir Himalaya

This paper presents a study on the Wular Lake which is the largest fresh water tectonic lake of Kashmir Valley, India. One hundred and ninety-six (196) water samples and hundred (100) sediment samples (n = 296) have been collected to assess the weathering and Anthropogenic impact on water and sediment chemistry of the lake. The results showed a significant seasonal variability in average concentration of major ions being highest in summer and spring and lower in winter and autumn seasons. The study revealed that lake water is alkaline in nature characterised by medium total dissolved solids and electrical conductivity. The concentration of the major ion towards the lake central showed a decreasing trend from the shore line. The order of major cations and anions was Ca2+ > Mg2+ > Na+ > K+ and HCO3 − > SO4 2− > Cl−, respectively. The geochemical processes suggested that the chemical composition lake water is mostly influenced by the lithology of the basin (carbonates, silicates and sulphates) which had played a significant role in modifying the hydrogeochemical facies in the form of Ca–HCO3, Mg–HCO3 and hybrid type. Chemical index of alteration values of Wular Lake sediments reflect moderate weathering of the catchment area. Compared to upper continental crust and the post-Archean Shale, the sediments have higher Si, Ti, Mg and Ca contents and lower Al, Fe, Na, K, P, Zn, Pb, Ni, Cu content. Geoaccumulation index (Igeo) and US Environmental Protection Agency sediment quality standards indicated that there is no pollution effect of heavy metals (Zn, Mn, Pb, Ni and Co).The study also suggested that Wular Lake is characterised by both natural and anthropogenic influences.

Solid‐State Reversible Quadratic Nonlinear Optical Molecular Switch with an Exceptionally Large Contrast

Exceptional nonlinear optical (NLO) switching behavior, including an extremely large contrast (on/off) of ∼35 and high NLO coefficients, is displayed by a solid-state reversible quadratic NLO switch. The favorable results, induced by very fast molecular motion and anionic ordering, provides impetus for the design of a novel second-harmonic-generation switch involving molecular motion.

Role of anion ordering in the coexistence of spin-density-wave and superconductivity in (TMTSF)2ClO4

Using various transport and magnetotransport probes, we study the coexistence of spin-density wave and superconductor states in (TMTSF)2ClO4 at various degrees of ClO4 anions ordering. In the two-phase complex state when both superconductivity and spin-density wave are observed in transport, we find prehistory effects, enhancement of the superconducting critical field, and strong spatial anisotropy of the superconducting state. These features are inconsistent with the conventional model of structural inhomogeneities produced by anion ordering transition. We reveal instead that superconductor and spin-density wave regions overlap on the temperature—dimerization gap V phase diagram, where V is varied by anion ordering. The effect of anion ordering on (TMTSF)2ClO4 properties is thus analogous to that of pressure on (TMTSF)2X (X = PF6 or AsF6), thereby unifying general picture of the coexistence of superconductivity and spin-density wave in these compounds.

Ion-Specific Conformational Behavior of Polyzwitterionic Brushes: Exploiting It for Protein Adsorption/Desorption Control

The conformation of polyzwitterionic brushes plays a crucial role in the adsorption/desorption of proteins on solid surfaces. By use of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR), we have systematically investigated the conformational behavior of poly(sulfobetaine methacrylate) (PSBMA) brushes as a function of ionic strength in the presence of different ions. The frequency change demonstrates that the effectiveness of anions to weaken the inter/intrachain association and to enhance the hydration of the grafted chains increases from kosmotrope to chaotrope in the low ionic strength regime, but the ordering of anions is almost reversed at the high ionic strengths. The dissipation change indicates that some heterogeneous structures are formed inside the brushes in the presence of chaotropic anions with the increase of ionic strength. In SPR studies, the change of resonance unit (ΔRU) with ionic strength is determined by the balance between the increase of thickness and the decrease of refractive index of the brushes. No anion specificity is observed in the SPR measurements because ΔRU is insensitive to the coupled water molecules inside the brushes. For the control of protein adsorption/desorption, our studies show that the brushes can more effectively resist the protein adsorption in the presence of a more chaotropic anion and a more chaotropic anion can also more effectively induce the protein desorption from the surface of the brushes. In addition, no obvious cation specificity can be observed in the conformational change of the brushes in either QCM-D or SPR measurements.

Experimental and Theoretical Study of the n‐Doped Successive Polyanions of Oligocruciform Molecular Wires: Up to Five Units of Charge

The electronic structure of polyanions of sterically encumbered triisopropylsilyl-substituted linear and cyclic oligo(phenyleneethynylene)s (Monomer, Trimer, Pentamer, and Triangle) is investigated by electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and UV/Vis-near-infrared (NIR) spectroscopies, cyclic voltammetry, and theoretical calculations (DFT). Increasing anion orders are generated sequentially in vacuo at room temperature by chemical reaction with potassium metal up to the pentaanion. The relevance of these compounds acting as electron reservoirs is thus demonstrated. Even-order anions are EPR silent, whereas the odd species exhibit different signatures, which are identified after comparison of the measured hyperfine couplings by ENDOR spectroscopy with those predicted by DFT calculations. With increasing size of the oligomers the electron spin density is first distributed over the backbone carbon atoms for the monoanions, and then further localized at the outer phenyl rings for the trianion species. Examination of the UV/Vis-NIR spectra indicates that the monoanions (T(.-) , P(.-) ) exhibit two transitions in the Vis-NIR region, whereas a strong absorption in the IR region is solely observed for higher reduced states. Electronic transitions of the neutral monoanions and trianions are redshifted with increasing oligomer size, whereas for a given oligomer a blueshift is observed upon increasing the charge, which suggests a localization of the spin density.

Opportunities for improved TBC durability in the CeO2–TiO2–ZrO2 system

A previously unreported, relatively large single-phase tetragonal field with exceptional tetragonality has been stabilized up to at least 1350°C by co-doping zirconia (ZrO2) with ceria (CeO2) and titania (TiO2). The tetragonality is believed to be responsible for an increase in micro-indentation toughness, relative to traditional 7YSZ, based on activation of ferroelastic domain switching. Evidence consistent with this toughening mechanism has been directly observed via transmission electron microscopy (TEM). Within grains >5μm, long-range anion order is induced within elastically switched domains. This observation provides additional insight on the toughening mechanism. In the absence of stoichiometric anion vacancies, the large non-transformable tetragonal composition range and the improved toughness suggest that this system could be a promising option for next generation thermal barrier coatings.

Structure and energetics of gas phase halogen-bonding in mono-, bi-, and tri-dentate anion receptors as studied by BIRD

Complexes of mono-, bi- (RB), and tridentate (RT) receptors with a range of anions (Cl(-), Br(-), I(-), NO3(-), H2PO4(-), HSO4(-), and tosylate (TsO(-))) have been studied in the gas phase by both experimental and theoretical methods. Temperature dependent blackbody infrared radiative dissociation (BIRD) experiments were performed on complexes of C8F17I with Br(-) and I(-), RB with I(-), NO3(-), HSO4(-), H2PO4(-), and TsO(-), and RT with I(-), HSO4(-) and TsO(-) and the observed Arrhenius parameters are reported here. Master equation modeling of the BIRD kinetics data was carried out to determine threshold dissociation energies. Geometry optimizations and thermochemistry calculations were performed using the B3LYP/6-31+G(d,p) level of theory. Additional single point energies were calculated using MP2/6-311++G(2d,p). Results were examined in terms of the binding order of various anions as well as the added binding strength from additional halogen bonding (XB) interactions. The relative binding energies of ions were generally consistent with the ordering previously reported from solution phase experiments; however, the relatively strong binding of H2PO4(-) to the bidentate receptor contrasted the solution phase observation of oxoanions having weaker interactions when compared to halides. An increase in the energy required to remove the same anion from the tridentate receptor when compared to the bidentate and monodentate receptors is explained as being due to the increase in halogen bonding interactions. The possibility of mixed halogen and hydrogen bonded complexes were considered.

Insights into the interplay between molecular structure and diffusional motion in 1-alkyl-3-methylimidazolium ionic liquids: a combined PFG NMR and X-ray scattering study

We report on how the local structure and the diffusional motion change upon increasing the alkyl chain length in 1-alkyl-3-methylimidazolium cation ionic liquids. This study has been performed by combining pulse field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and small angle X-ray scattering (SAXS) experiments. The cationic side chain length varies from ethyl (n = 2) to hexadodecyl (n = 16), while the anion is always bis(trifluoromethanesulfonyl)imide (TFSI). We find that the self-diffusivity of the individual ionic species is correlated to the local structure in the corresponding ionic liquid, namely the nano-segregation into polar and non-polar domains. In agreement with previous results, we observe that for relatively short alkyl chains the cations diffuse faster than the anions; however we also note that this difference becomes less evident for longer alkyl chains and a cross-over is identified at n ≈ 8 with the anions diffusing faster than the cations. Our results indicate that this controversial behavior can be rationalized in terms of different types of cation-cation and anion-anion orderings, as revealed by a detailed analysis of the correlation lengths and their dispersion curves obtained from SAXS data. We also discuss the validity of the Stokes-Einstein relation for these ionic liquids and the evolution of the extrapolated cationic radius that was found to depend non-strictly linearly on n, in agreement with the cation-cation correlation lengths.

Anion-ordered chains in a d1 perovskite oxynitride: NdVO2N

The correlated anion order in the oxynitride perovskite NdVO(2)N, where disordered zig-zag VN chains segregate into planes within a pseudo-cubic lattice, is similar to that in materials such as SrTaO(2)N containing d(0) transition metal cations. However, NdVO(2)N has 3d(1) V(4+) cations and the 3d-electrons are itinerant, showing that the anion chain order in oxynitride perovskites is robust to electron-doping.

Ab initio molecular dynamics simulations of ion–solid interactions in Gd2Zr2O7 and Gd2Ti2O7

The development of the ab initio molecular dynamics (AIMD) method has made it a powerful tool in describing ion–solid interactions in materials, with the determination of threshold displacement energies with ab initio accuracy, and prediction of a new mechanism for defect generation and new defective states that are different from classical molecular dynamics (MD) simulations. In the present work, this method is employed to study the low energy recoil events in Gd2Zr2O7 and Gd2Ti2O7. The weighted average threshold displacement energies in Gd2Zr2O7 are determined to be 38.8 eV for Gd, 41.4 eV for Zr, 18.6 eV for O48f, and 15.6 eV for O8b, which are smaller than the respective values of 41.8, >53.8, 22.6 and 16.2 eV in Gd2Ti2O7. It reveals that all the ions in Gd2Zr2O7 are more easily displaced than those in Gd2Ti2O7, and anion order–disorder is more likely to be involved in the displacement events than cation disordering. The average charge transfer from the primary knock-on atom to its neighbors is estimated to be ∼0.15, ∼0.11 to 0.27 and ∼0.1 to 0.13 |e| for Gd, Zr (or Ti), and O, respectively. Neglecting the charge transfer in the interatomic potentials may result in the larger threshold displacement energies in classical MD.

Aluminum ordering and clustering in Al-rich synthetic phlogopite: The influence of fluorine investigated by 29Si CPMAS NMR spectroscopy

The influence of fluorine on cationic and anionic ordering in the mica mineral phlogopite has been investigated using 29Si, 1H, and 19F MAS as well as {1H}/{19F} → 29Si CPMAS and CP-depolarization NMR spectroscopies. It can be shown that the mere presence of fluorine achieves a tremendous loss of capability to incorporate aluminum into the phlogopite structure. Fluorine is usually located in Mg-rich octahedral and Si-rich tetrahedral clusters of the phlogopite structure while hydroxyl groups are located in Al-rich octahedral and tetrahedral clusters as derived from {1H}/{19F} → 29Si CPMAS NMR spectroscopies. The ordering effect in these two basic structural clusters can also be proven by a smaller 29Si linewidth in the {19F} → 29Si CPMAS NMR experiments compared to the usual 29Si MAS NMR experiment showing a stronger ordering of Si environments near the two different anion types fluorine and hydroxyl. Intensities of the {1H}/{19F} → 29Si CPMAS NMR signals as function of the contact-time show a deviation from the classical I-S model and can be attributed to the I - I *- S model. Time constants like the proton/fluorine spin diffusion time ( T df ), the spin-spin relaxation time ( T 2), the λ parameter (λ), and the proton/fluorine spin-lattice time in the rotating frame ( T 1ρ) were extracted to give information about the local structure.

High-temperature order–disorder transitions in the skutterudites CoGe1.5Q1.5 (Q=S, Te)

The temperature dependence of anion ordering in the skutterudites CoGe1.5Q1.5 (Q=S, Te) has been investigated by powder neutron diffraction. Both materials adopt a rhombohedral structure at room temperature (space group R3¯ ) in which the anions are ordered trans to each other within Ge2Q2 rings. In CoGe1.5S1.5, anion ordering is preserved up to the melting point of 950°C. However, rhombohedral CoGe1.5Te1.5 undergoes a phase transition at 610°C involving a change to cubic symmetry (space group Im3¯). In the high-temperature modification, there is a statistical distribution of anions over the available sites within the Ge2Te2 rings. The structural transition involves a reduction in the degree of distortion of the Ge2Te2 rings which progressively transform from a rhombus to a rectangular shape. The effect of this transition on the thermoelectric properties has been investigated.

High performance ion chromatography of transition metal chelate complexes and aminopolycarboxylate ligands

A simple ion chromatographic method was developed for the separation of transition metal chelates (CuEDTA, CuDCTA, ZnEDTA, ZnDCTA) and free anionic complexing ligands (EDTA, DCTA) using alkaline carbonate eluents and conductivity detection. The complex equilibria and kinetic process of separations were studied in order to understand major factors in the control of selectivity and retention order of complex anions. A systematic study was applied to identify the additional peaks of the system as NaEDTA3−, NaHEDTA2−, Na2EDTA2−, EDTA4−/HEDTA3−, DCTA4−/HDCTA−3. On the basis of microequilibrium considerations of chelating ligand, it was shown that one should expect the peaks of sodium chelates when the ligand is in excess in the sample solution. The probability density function was introduced for calculation of complex chromatograms, because complexing ligands can exist in at least two different interconvertible forms in the presence of metal ion. The chromatogram of interconverting chelate species can be given as the sum of probability density functions (P) weighed by the molar fractions of complexed (ΦML) and dissociated (ΦL) forms. The influences of kinetic rate of complex formation and dissociation on the distribution of components between eluents and ion exchange stationary phases were quantitatively described and demonstrated by elution profiles. The applicability of the developed method is represented by the simultaneous analysis of transition metal chelates and inorganic anions. ICP-AES analysis and FTIR-ATR technique were used for confirmation of IC results for metals and ligands, respectively. Collection protocols for the heart-cutting procedure of chromatograms were applied in the analysis of target components. The limit of detection and linearity of the method in the range of 0.01–0.25mM sample concentration were also presented.

First-Principles Study on Relaxor-Type Ferroelectric Behavior without Chemical Inhomogeneity in BaTaO2N and SrTaO2N

The wide range of applications attracts interest in oxynitride perovskites. BaTaO2N and SrTaO2N have relaxor-type high dielectric permittivities and are promising candidates in many applications especially because Pb is not included, unlike in many relaxor ferroelectrics. There is an urgent need to understand the relation between the anion ordering and the permittivity to facilitate screening and designing materials with higher permittivity, and the chemistry that results in relaxor-type behavior without chemical inhomogeneity. We show using systematic first-principles calculations that stable anion orderings in BaTaO2N and SrTaO2N have two kinds of similar, 3D −Ta–N– coiled chain motifs that can switch to each other, forming a mechanism to break long-range order and increasing the diversity of anion orderings around the pentavalent Ta. Both materials have two sets of low-energy displacements forming opposite polarization directions that can be easily alternated at the picosecond scale. This explanation o...

Influence of dyeing auxiliaries on AB74 dye degradation by UV/H2O2 process

The effect of dyeing auxiliaries on UV/H2O2 removal of an indigoid dye, Acid Blue 74 (AB74) from the solution was investigated. The inhibition effect of anions including carbonate, bicarbonate and chloride on the process efficiency was evaluated in terms of color removal and total organic carbon (TOC) abatement. The presence of carbonate, bicarbonate and chloride anions had no considerable effect on the total decolorization time. However, the degradation efficiency of the process was enhanced by bicarbonate anion during the first 80 min of the process. During this period, the formation of active oxygen species such as CO3−,HCO4−andO2− that participate in the degradation process of AB74 increases the degradation rate, in spite of the consumption of hydroxyl radicals by these anions. After this period, the overall efficiency was considerably decreased. Adding the chloride had less decreasing effect compared to the bicarbonate. The order of anions as AB74 degradation inhibitor in this study could be concluded as: Cl−<HCO3−≈(HCO3−+Cl−).

Phosphorus removal from wastewater using nano-particulates of hydrated ferric oxide doped activated carbon fiber prepared by Sol–Gel method

Sol–Gel method is used to immobilize nano-particulates of hydrated ferric oxide (HFO) within macroporous activated carbon fibers (ACFs), and the phosphate removal behavior and its mechanisms of the new hybrid phosphate adsorbent named as ACF-NanoHFO are studied. The surface structure of ACF-NanoHFO is characterized by scanning electron microscopy (SEM), showing Sol–Gel method to be a reliable method for improving performances of depositing iron nano-particles on the ACF. The Freundlich and Langmuir models are used to simulate the sorption equilibrium, indicating that the Langmuir model is more suitable than the Freundlich model for well elucidation of the experimental data. The maximum adsorption capacity is calculated to be 12.86mg/g. The kinetic data from the adsorption of phosphate are discussed in a framework of the pseudo second-order model, indicating that the adsorption of phosphate is a chemisorption process. The phosphate adsorption is highly pH dependent. The coexistence of other anions in solutions has an adverse effect on phosphate adsorption. A decrease in adsorption capacity follows the order of exogenous anions, i.e., F->NO3->Cl->SO42-. The ligands exchange and electrostatic interactions are manifested to be two main mechanisms for phosphate adsorption of ACF-NanoHFO revealed by Fourier transform infrared (FT-IR) spectroscopy and change of pH values associated with the adsorption process. All the results indicate that the ACF-NanoHFO has a considerable potential for the phosphate removal from contaminated waters.

Crystallographic analysis of microtwin structures of sulfides: The case study of lillianite and heyrovskyite

Crystal structures of the minerals lillianite Pb3Bi2S6 and heyrovskyite Pb6Bi2S9 are subjected to crystallographic analysis to demonstrate that the microtwinning of the structure-forming 2D layer fragments occurs within common cation and anion matrices. A combination of the PbS-type structural fragments with different orientations is achieved by vacant sites in the cation and anion translational sublattices without their noticeable distortion. In the structure of β-Pb3Bi2S6 (the high-pressure phase of lillianite), the pseudo-translational ordering of cations and anions as well as the overall symmetry of the structure are significantly lowered, while the general arrangement is preserved.

First principles calculation of the electronic properties and lattice dynamics of Cu2ZnSn(S1−xSex)4

Using density functional theory, we calculated the electronic structure, the lattice dynamics, and the Raman spectra of Cu2ZnSn(S1−xSex)4, (CZTSSe) an emerging photovoltaic material for thin-film solar cells. In particular, we investigated the effects of the local arrangement of S and Se within the unit cell on the electronic properties of these materials. We find that the S-to-Se ratio (e.g., x) and the spatial distribution of the anions in the unit cell can significantly alter the band structure. In particular, the S-to-Se ratio and anion distribution determine the energy splitting between the electronic states at the top of the valence band and the hole mobility in CZTSSe alloys and solar cells. Moreover, we find that x-ray diffraction patterns and phonon dispersion curves are sensitive to the local anion ordering. The predicted Raman scattering frequencies and their variation with x agree with experimentally determined values and trends.