Cationic Substituents Research Articles

Strain-Modified Oxygen Transport in Rare-Earth Substituted Ceria: Migration Direction and Defect Association

Traditionally, the search for new electrolytes and electrodes for ionic devices with improved properties has been focused on compositional tuning and the search for new functional oxides. Recently, there has been increasing interest on the interplay of the chemical, electrical, and mechanical properties in electroceramic materials, referred to as electro-chemo-mechanics. This approach may offer a route to better than state-of-the-art materials making use of composites, nanoscale design, and engineered interfaces.In particular, perturbing the crystal lattice away from the equilibrium structure via an applied lattice strain has been investigated from some time as a method to realise considerable improvements in oxygen-ion conductivity. Interest in this approach has, however, waned over recent years for two primary reasons: (i) a lack of consistency and reproducibility in the reported experimental findings and (ii) typically only modest changes in ionic transport are observed. In this presentation, we will address both reasons and make the case for lattice strain still being a promising route to enhanced oxygen transport.By using an unconventional method of thermally annealing out strain which occurs during deposition of epitaxial rare earth-substituted films grown by pulsed laser deposition (PLD), we were able to tailor the strain with no influence from grain boundaries or interfaces (Figure 1a). The full strain states of the films, both out-of-plane and in-plane, as characterised by high-resolution X-ray diffraction, could be correlated with changes in the magnitude and activation energies of ionic conduction (Figure 1b). Through careful analysis of the literature, we managed, for the first time, to develop a quantitative consensus on the variation of the transport properties of ceria as a function of lattice strain, across both experimental and computational reports. Furthermore, by comparing the transport properties both in-plane and out-of-plane, we were able to experimentally demonstrate the effects of migration direction with respect to the biaxially strained plane (Figure 1c).By investigating the substituent rare-earth cation, we were also able to vary the influence of defect-association on the ionic conductivity. Comparing La-, Gd-, and Yb-substituted ceria, we find that the change in activation energy with strain is dependent on the size of the dopant cation (Figure 1d), indicating that strain-modified conductivity is dependent both on the migration edge barrier and the defect-association. These findings give unique insights into the atomistic interaction of strain on the ionic transport of oxygen in substituted CeO2, and suggest that substantially improved conductivity in strained oxides may yet still be achieved if migration direction and defect association are optimised.Figure 1 - (a) XRD peaks from the (004) out-of-plane reflection and (b) variation in the ionic conductivity of Gd-substituted films as a function of annealing temperature. (c) Schematic of a biaxially-strained CeO2 unit cell with out-of-plane and in-plane migration directions labelled. (d) Effect of strain on the out-of-plane and in-plane activation energies of conduction for Gd and Yb substituents. Figure 1

Synthesis, structure and photochromic properties of indoline spiropyrans with electron-withdrawing substituents

Indoline spiropyrans containing conjugated cationic vinyl-3H-indolium fragment and their analogues with formyl substituent in the 2H-chromene moiety were synthesized by a simple one-pot method. The structure of the obtained compounds was confirmed by 1H and 13C NMR (including 2D methods) and IR spectroscopy, as well as by element analysis and HRMS. Molecular structures of 1,3,3,6´-tetramethyl-8´-formyl-spiro[indoline-2,2´-2H-chromene] 8 and its cationic derivative 5 were refined by single crystal X-ray and compared. Notably, it was found that the crystals of formyl-substituted spiropyran contain both enantiomers (R- and S-) of the molecule in the unit cell. Photochromic properties of all the compounds were studied and compared using spectral-photokinetic methods. It was found out that electron-withdrawing substituents (vinyl-3H-indolium fragment and formyl group) located at the position 6´ of 2H-chromene moiety stabilize merocyanine isomer more effectively, than at the position 8´, leading even to the appearance of negative photochromism for the compound 3 with cationic substituent, which is quite unusual for this class of organic photochromes. Also, it was shown that chlorine atoms as σ-acceptors at the positions 5 and 5´´ of hetarene moiety and cationic fragment can suppress photochromic behavior.

A fundamental assessment of the impacts of cation (Cd, Co, Fe) substitution on the molecular chemistry and surface reactivity of sphalerite

A series of cadmium-, cobalt-, and iron-substituted (0–4 wt%) sphalerite mineral samples were synthesised to test how the presence of these cation substituents alter the crystal structure, surface bonding environment and electronic properties of sphalerite and to illustrate how these alterations impact the electrokinetic behaviour of mineral surfaces under conditions relevant to sphalerite flotation. A combination of X-ray Diffraction (XRD), Raman and ultraviolet–visible spectroscopies, and zeta potential experiments were used to demonstrate these impacts. XRD results showed a positive correlation between the measured lattice distortions and the ionic size and concentration of the respective cation substituents. Raman results confirmed the presence of new metal-sulphur (M−S) bonds within the ZnS host cluster reflected by a new impurity mode which correlates to the concentration and chemical nature of the cation substituents. The presence of metal substituents further induced a change in the band gap of sphalerite which reduced according to Cd > Fe > Co. These measurements informed the effect of the molecular characteristics of impurity-bearing sphalerite on the electrokinetic response of sphalerite in the presence of CuSO4 and xanthate collector. Cobalt-bearing sphalerites which have the lowest band gap and greatest distortions to molecular and crystal structure had the most notable impact on zeta potential measurements. A small increase in Co concentration induced a larger shift in point of zero charge for collectorless activation but did not impact the collector interactions. Conversely, Cd which has a wider band gap is less electronegative than Co exhibited the reverse behaviour. This study thus details how the presence of cation substituents modifies sphalerite bulk structure, in turn impacting its surface bonding environment and electronic properties, and ultimately exerting a notable control on flotation chemistry.

Theoretical and experimental studies of ionic liquid-urea mixtures on chitosan dissolution: Effect of cationic structure

Two imidazolium chloride ionic liquids (ILs) were mixed with urea for chitosan dissolution. Ionic liquids were [Amim]Cl and [Etmim]Cl (1-allyl-3-methyl-imidazolium chloride and 3-methyl-1-(ethylacetyl)imidazolium chloride, respectively). Physicochemical properties of neat ILs and IL-Urea solutions (including density, viscosity, conductivity, β value, π* value, and thermogravimetric analysis), were thoroughly investigated. Dissolution performance of chitosan in IL-Urea solutions was determined.Chitobiose (KET) as model chitosan structure, density functional theory (DFT) calculations were used to discuss the interactions between IL, urea, and chitobiose, and to clarify the different physicochemical properties of ILs, IL-Urea solutions. Also DFT simulation results were used for elucidating the influence of different cationic substituents and urea addition for chitosan dissolution.[Etmim]Cl showed higher density, viscosity, conductivity, β, and π* value than those of [Amim]Cl. These results revealed strong hydrogen bonds among [Etmim]Cl owing to the carboxylic acid ester group than allyl group of [Amim]Cl. Densities, viscosities, and π* values of IL-Urea solutions increased with increasing urea content. Conductivities and β values of IL-Urea solutions decreased with the increase of urea content at same temperature. The thermal stability of [Amim]Cl-Urea mixture increased when urea content increased from 10% to 30%, which was different from [Bmim]Cl-Urea melt. The thermal stability of [Etmim]Cl-Urea mixture was different to that of [Amim]Cl-Urea mixture.Urea was accommodated in ILs, forming hydrogen bonds with both the anion and cation in ILs, which changed the molecular interactions of ILs. The influence of different substituents in imidazolium ILs and urea addition on chitosan dissolution were analyzed using experimental determination and DFT calculations. Cationic substituents of imidazolium ILs play an extraordinary role in hydrogen bonds formation with chitobiose, so to strengthen chitosan dissolution. The information obtained would provide a guide for designing novel IL solvent systems for chitosan dissolution.

Сationic carboxamide derivatives of tricyclic heteroaromatic compounds: synthesis and preliminary evaluation of antiproliferative activity

This research was aimed at the synthesis and study of biological activity of the carboxamides of tricyclic heteroaromatic systems, acridone, phenazine and thioxanthone, containing the aliphatic and aromatic cationic substituents at amide fragment. These heterocyclic cores are DNA intercalating agents, whereas the introduction of cationic groups provides additional ionic interactions of the ligands with their biological targets, such as DNA and enzymatic complexes of the system of nucleic acids biosynthesis. A convenient way of the introduction of such groups is a modification of heterocyclic carboxamides. A small library of new cationic amide derivatives of acridone-4-, phenazine-1- and thioxanthone-4-carboxylic acids was obtained. They were synthesized in 37-81% yield by mild and selective quaternization of the nitrogen atoms at N,N-dimethylaminoalkyl (alkyl = ethyl, propyl) and pyridylmethyl fragments of the neutral N-functionalized carboxamides with methyl iodide. Tricyclic heteroaromatic cores were not affected. Convenient protocol for the synthesis of thioxanthone-4-carboxylic acid (TCA) based on the reaction of 2-mercaptobenzoic and 2-iodobenzoic acids followed by cyclization of the intermediate was developed (yield 79%). A series of new N-functionalized neutral amides of TCA, the precursors of corresponding cationic carboxamide, were also obtained via the reaction of acyl chloride with amines. Preliminary in vitro testing of four compounds as potential antitumor agents in U87MG tumor cell culture (human malignant glioma) demonstrated their significant antiproliferative activity at low micromolar concentrations, with growth inhibition values GI50 in the range 1.7-11 µM. These results suggest that cationic carboxamides of tricyclic heteroaromatic systems are promising scaffolds for the design of new antitumor drugs.

Band-Gap Engineering of Mo- and W-Containing Perovskite Oxides Derived from Barium Titanate

Ferroelectric oxide perovskites are promising materials for use in photovoltaic devices, due to their ability to exploit the bulk photovoltaic effect to achieve high power-conversion efficiency. In this work, we use first-principles methods to investigate the ferroelectric perovskite $[{\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_{3}{]}_{x}\text{\ensuremath{-}}[{\mathrm{Na}\mathrm{Ti}}_{1/2}{\mathrm{Mo}}_{1/2}{\mathrm{O}}_{3}{]}_{1\ensuremath{-}x}$ and $[{\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_{3}{]}_{x}\text{\ensuremath{-}}[{\mathrm{Na}\mathrm{Ti}}_{1/2}{\mathrm{W}}_{1/2}{\mathrm{O}}_{3}{]}_{1\ensuremath{-}x}$ solid solutions for potential use in ferroelectric-based photovoltaics. We find that compositional variations change the band gap, shifting it to the edge of the visible range for the 25% ${\mathrm{Na}\mathrm{Ti}}_{1/2}{\mathrm{Mo}}_{1/2}{\mathrm{O}}_{3}$ composition and to the visible range for some Mo-cation and W-cation arrangements for the 50% ${\mathrm{Na}\mathrm{Ti}}_{1/2}{\mathrm{Mo}}_{1/2}{\mathrm{O}}_{3}$ and 50% ${\mathrm{Na}\mathrm{Ti}}_{1/2}{\mathrm{W}}_{1/2}{\mathrm{O}}_{3}$ compositions. Mo and W substitutions both maintain the ferroelectric properties of the parent ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_{3}$. While the A-site cation arrangement has a minor effect on the band gap, the variations in the B-site cation arrangement and the cation displacements affect the band gap by up to 0.8 eV. Analysis of the structures and the calculated band-gap values shows that the band gap is controlled by the identity of the substituent cation, the O-B-O angles, the relative orientations of the Mo and W substituent atoms, and the B-cation displacement. We demonstrate the thermodynamic feasibility of these solid solutions by formation energy analysis. The decrease of the band gap relative to the parent ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_{3}$ to the standard and transparent photovoltaic range combined with the ferroelectricity maintained make this earth-abundant-containing solid solution a promising candidate for use in high-performance ferroelectric-based photovoltaic devices.

Effect of periphery cationic substituents of porphyrin on the B-Z transition of poly[d(A-T)2], poly[d(G-C)2] and their binding modes

The binding mode of cationic porphyrin (trans-BMPyP) with poly[d(G-C)2] and poly[d(A-T)2] was examined according to the site of the periphery cationic methyl pyridine ion of the cationic porphyrin (o-, m-, p-) as well as the possibility of a B-Z transition depending on the binding modes by measuring the absorption spectrum and circular dichroism (CD). The negative band found in the soret region showed the intercalation mode of m- and p-trans-BMPyP-poly[d(G-C)2] to the DNA base pairs, but no B-Z transition was induced. On the other hand, the distinctive bisignate band found in the soret region of the CD spectrum for m- and p-trans-BMPyP-poly[d(A-T)2] suggests that m- and p-trans-BMPyP have an effective extensive stacking-based binding mode along with the skeleton of poly[d(A-T)2], wherein the B-Z transition was induced through extensive stacking. The difference in binding mode was attributed to the difference in the molecular structure depending on the site of the periphery cationic methyl pyridine ion in the cationic porphyrin. In other words, o-trans-BMPyP is nonplanar because of the steric hindrance of the cationic methyl pyridine ion at the o-site. In contrast, m- and p-trans-BMPyP are planar, but not all porphyrins with a planar structure undergo the B-Z transition. In conclusion, a B-Z transition is induced if the structure of a porphyrin is planar and the binding mode allows the porphyrins to be stacked effectively along the DNA skeleton, not in a binding mode where the porphyrin is intercalated to the DNA.Communicated by Ramaswamy H. Sarma

Effect of cation substituent of dodecanesulfate-based anionic surface active ionic liquids on micellization: Experimental and theoretical studies

Anionic surface active ionic liquid (SAIL), 1-butyl-3-ethoxycarbonylimidazolium dodecanesulfate ([Etbim][C12H25SO4]) was synthesized. The dependence of micellization of dodecanesulfate-based anionic SAILs on cation substituents of anionic SAILs was analyzed using experimental and theoretical studies. Critical micelle concentration of [Etbim][C12H25SO4] was 1.17 mmol/L at 298.15 K. [Etbim][C12H25SO4] showed superior surface property than [Bmim][C12H25SO4] with same dodecanesulfate anion.Theoretical density functional theory (DFT) calculation was used to determine the micellization tendency of anionic SAILs ([Bmim][C12H25SO4] and [Etbim][C12H25SO4]). CMC difference of [Etbim][C12H25SO4] and [Bmim][C12H25SO4] was ascribed to the electrostatic interaction (repulsion or attraction) and hydrophobic interaction of cations ([Bmim]+ and [Etbim]+), dodecanesulfate anion, anionic SAILs ([Bmim][C12H25SO4] or [Etbim][C12H25SO4]), and the interactions toward water molecules in aqueous solution. The hydrocarbon chain lengths of [Bmim]+ and [Etbim]+ reflected the different hydrophobic interaction of cations, which clarified that the important role of cation substituents on micellization of [Etbim][C12H25SO4] and [Bmim][C12H25SO4]. Atomic charge distribution of cations will play important role on the further hydration toward water molecules or electrostatic attraction toward [C12H25SO4]− anion. Typical hydrogen bonds and charge changes of typical atoms were beneficial for electrostatic attraction and electrostatic repulsion between polar groups of SAILs. The electrostatic repulsion and electrostatic attraction between polar groups of SAILs affected the CMC values of [Bmim][C12H25SO4] and [Etbim][C12H25SO4]. Changes of binding energy (D0) and difference of binding energy (ΔD0) confirmed the tendency of [Etbim][C12H25SO4] micelle formation was higher than that of [Bmim][C12H25SO4].

Influence of the Sc cation substituent on the structural properties and energy transfer processes in GAGG:Ce crystals

Modification of band structure induced by Sc in a novel material Gd2.97Ce0.03Ga2.5Sc1Al1.5O12 results in the enhancement of energy transfer to Ce3+.

Physical properties of new ordered bimetallic phases M0.25Cd0.75PS3 (M = ZnII, NiII, CoII, MnII).

Four bimetallic phases of the thiophosphate family have been synthesized by the cationic exchange reaction using a freshly prepared K0.5Cd0.75PS3 precursor phase and methanolic solutions of nitrates of the divalent cations ZnII, NiII, CoII, and MnII. All the materials were characterized by FTIR, PXRD, SEM-EDXS and (in the case of the diamagnetic compounds) by solid state NMR. For the K0.5Cd0.75PS3 precursor, the X-ray powder diffraction data suggest a modification of the structure, while solid state NMR results confirm that this phase possesses an ordered arrangement of Cd vacancies. The cationic exchange reaction achieves a complete removal of potassium ions (no potassium detected by SEM-EDXS) and re-occupation of the vacancies by divalent cations. Therefore, the obtained compounds have an average composition of M0.25Cd0.75PS3 (M = ZnII, NiII, CoII, MnII) and possess an ordered distribution of the substituent cations. Even with the paramagnetic substitution level of 25%, antiferromagnetic behaviour is present in the phases with MnII, CoII and NiII, as evidenced by dc susceptibility and in the case of the MnII substituted phase by EPR. The cooperative magnetic interactions confirm the conclusion that the paramagnetic ions adopt an ordered arrangement. The analysis by broad band impedance spectroscopy allows to attribute the conductivity in these materials to charge movements in the layers due to the difference in electronegativity of the metal ions. Zn0.25Cd0.75PS3 is the phase that shows the highest conductivity values. Finally, the band gap energies of the bimetallic phases tend to be lower than those of the single-metal phases, probably due to an overlap of the band structures.

Electronic Tuning of Mixed Quinoidal-Aromatic Conjugated Polyelectrolytes: Direct Ionic Substitution on Polymer Main-Chains.

The synthesis of conjugated polymers with ionic substituents directly bound to their main chain repeat units is a strategy for generating strongly electron-accepting conjugated polyelectrolytes, as demonstrated through the synthesis of a series of ionic azaquinodimethane (iAQM) compounds. The introduction of cationic substituents onto the quinoidal para-azaquinodimethane (AQM) core gives rise to a strongly electron-accepting building block, which can be employed in the synthesis of ionic small molecules and conjugated polyelectrolytes (CPEs). Electrochemical measurements alongside theoretical calculations indicate notably low-lying LUMO values for the iAQMs. The optical band gaps measured for these compounds are highly tunable based on structure, ranging from 2.30 eV in small molecules down to 1.22 eV in polymers. The iAQM small molecules and CPEs showcase the band gap reduction effects of combining the donor-acceptor strategy with the bond-length alternation reduction strategy. As a demonstration of their utility, the iAQM CPEs so generated were used as active agents in photothermal therapy.

Electronic Tuning of Mixed Quinoidal‐Aromatic Conjugated Polyelectrolytes: Direct Ionic Substitution on Polymer Main‐Chains

AbstractThe synthesis of conjugated polymers with ionic substituents directly bound to their main chain repeat units is a strategy for generating strongly electron‐accepting conjugated polyelectrolytes, as demonstrated through the synthesis of a series of ionic azaquinodimethane (iAQM) compounds. The introduction of cationic substituents onto the quinoidal para‐azaquinodimethane (AQM) core gives rise to a strongly electron‐accepting building block, which can be employed in the synthesis of ionic small molecules and conjugated polyelectrolytes (CPEs). Electrochemical measurements alongside theoretical calculations indicate notably low‐lying LUMO values for the iAQMs. The optical band gaps measured for these compounds are highly tunable based on structure, ranging from 2.30 eV in small molecules down to 1.22 eV in polymers. The iAQM small molecules and CPEs showcase the band gap reduction effects of combining the donor‐acceptor strategy with the bond‐length alternation reduction strategy. As a demonstration of their utility, the iAQM CPEs so generated were used as active agents in photothermal therapy.

One-pot synthesis and the structure study of a new indoline spiropyran with cationic substituent

One-pot synthesis and the structure study of a new salt spiropyran of indoline series containing 2H-chromenic vinyl-3H-indolium fragment as a substituent at the position 8 are described. The structure was confirmed by the method of NMR 1H and 13C spectroscopy, IR and high-resolution mass spectrometry. The single crystals of the compound were investigated by X-ray analysis. The structure was compared with the previously known isostructural analogue [10].

One-Pot Synthesis and Structure Study of a New Indoline Spiropyran with Cationic Substituent

One-Pot Synthesis and Structure Study of a New Indoline Spiropyran with Cationic Substituent

Gas-Induced Ion-Free Stable Radical Anion Formation of Organic Semiconducting Solids as Highly Gas-Selective Probes.

The formation of stabilized radical anions on organic materials in the solid state is an important issue in radical-based fundamental research and various applications. Herein, for the first time, we report on gas-induced ion-free stable radical anion formation (SRAF) of organic semiconducting solids with high gas selectivities through the use of organic field-effect transistor (OFET) gas sensors and electron spin resonance spectroscopy. In contrast to the previously reported SRAF, which requires either anionic analytes in solution and/or cationic substituents on π-electron-deficient aromatic cores, NDI-EWGs consist of an n-type semiconducting naphthalene diimide (NDI) and various electron-withdrawing groups (EWGs) that exhibit non-ion-involved, gas-selective SRAF in the solid state. In the presence of hard Lewis base gases, NDI-EWG-based OFETs exhibit enhanced conductivity (Current-ON mode) through the formation of an SRAF NDI/gas complex, while in the presence of borderline and soft Lewis base gases, NDI-EWG-based OFETs show decreased conductivity (Current-OFF mode) by the formation of a resistive NDI/gas complex. Organic semiconducting solids with EWGs exhibiting highly gas-selective solid-SRAF constitute a very promising platform for radical-based chemistry and can be used in various applications, such as highly gas-selective probes.

Cobalt-Based Lithiated Spinel Oxide As a Novel Zero-Strain Cathode

Zero-strain electrode materials that exhibit extremely small volume changes during intercalation reactions provide unique opportunities for highly stable lithium batteries. In particular, intecalation-induced strain in electrodes is a major factor in the degradation of advanced lithium batteries. For example, recent studies of high-performance Ni-rich layered cathodes unequivocally show a clear correlation between particle fracture, due to anisotropic volume expansion of polycrystalline grains, and continuously increasing cathode impedance.[1] Such chemo-mechanical behavior of electrode materials is even more critical to all-solid-state batteries in which the solid-solid interface between the electrode and solid electrolyte is prone to cracking and disintegration, even with small volume mismatches during electrochemical cycling. The best known zero-strain electrode material is the Ti-based spinel, Li4Ti5O12, that has been developed as a stable anode. Recently, LiRh2O4 spinel has been reported as a zero-strain cathode that operates at 3.2 V vs. Li/Li+,[2] however, its practical use is limited by the high cost of the precious metal, rhodium. A more feasible zero-strain cathode candidate is the ‘low-temperature’ (LT) form of LiCoO2, which adopts a cubic, lithiated spinel structure, Li2[Co2]O4.[3,4] On lithium extraction, LT-LiCoO2 provides an attractive 3.6 V vs Li. However, despite the high operating voltage and minimal volume change, this zero-strain material has received little attention since its discovery because of its poor cycling stability. In this presentation we report that cation substitution greatly improves the electrochemical perperties of LT-LiCo1-xMxO2 electrodes (M = cations). The different effects of various cation substituents on electrode performance will be compared and the zero-strain intercalation mechanism in LT-LiCo1-xMxO2 will be discussed.

Structure and Luminescence Properties of (Y1 –хLaх)3(Al1 –уGaу)5O12:Ce3+ Substituted Garnets

The compounds of different composition with garnet structure, doped with Ce3+, have been obtained by co-precipitation method with use of partial substitution of Y3+ and Al3+ onto La3+ and Ga3+. The crystal structure of the substituted materials has been studied in detail by neutron diffraction. The nature and concentration of substituent cations have been shown to influence the structural parameters and luminescence spectra of (Y1 –хLaх)3(Al1 –уGaу)5O12:Ce3+ compounds. Changes in the geometry of the oxygen dodecahedra have the strongest effect on Ce3+ luminescence in the substituted materials.

Crystal Structures and Melting Behaviors of 2D and 3D Anionic Coordination Polymers Containing Organometallic Ionic Liquid Components.

Although coordination polymers generally do not melt, several that do melt have been synthesized recently and have drawn much attention. In this study, two- and three-dimensional coordination polymers that melt were synthesized, [Ru(Cp)(C6 H5 R)][M{C(CN)3 }2 ] (R=H, Me, Et; M=K, Rb; Cp=C5 H5 ), which are complex salts comprising M[C(CN)3 ] and organometallic ionic liquids [Ru(Cp)(C6 H5 R)][C(CN)3 ]. They have anionic [M{C(CN)3 }2 ]n - coordination polymer frameworks, whose dimensionalities depend on the size of the organometallic cation inside. Their melting points decreased with increasing cation substituent length and size of the alkali metal ion (Tm =102-239 °C), and these low-melting-point coordination polymers exhibited incongruent melting, forming mixtures of solid M[C(CN)3 ] and ionic liquid upon melting. Using the same method, coordination polymers were synthesized with various bridging ligands, [Co(Cp)2 ][MX2 ] (X=B(CN)4 , C(CN)3 , N(CN)2 ; M=K, Na), as well as a paramagnetic coordination polymer, [Fe(Cp)2 ][K{C(CN)3 }2 ].

Optical vibrational properties of Bi2-xCaxSn2O7-x/2 ceramics

Bi2-xCaxSn2O7-x/2 ceramics were synthesized by solid-state reactions and sintered at 1050 °C. Raman and infrared spectroscopies were used to investigate the optical vibrational properties of pure Bi2Sn2O7 ceramics, as well as to understand the influence of Ca2+ substitution for Bi3+ on the vibrational characteristics of the Bi2-xCaxSn2O7-x/2 system (for x ≤ 0.02). First, we demonstrate that partial substitution of Bi3+ with Ca2+ ions does not promote the β-phase, as it is commonly reported for other cationic substituents. The results of Raman and infrared spectroscopies showed that 34 bands were observed by Raman scattering, and 22 modes were observed by infrared spectroscopy. It was also verified that Raman scattering was quite sensitive to the morphological features of the samples, which was not the case for infrared spectroscopy. Scanning electron microscopy on the sintered samples showed that such sensitivity is partially linked to the grain sizes, which are larger than the incident light beamwidth, but smaller than the infrared beamwidth. Thus, infrared spectroscopy takes contributions from the average of a number of grains, while Raman spectroscopy evaluates contributions of single grains. The dielectric merit factors of the Bi2Sn2O7 ceramics were also obtained from infrared spectroscopy, namely ɛ0 = 24.2 and Qu×f = 56.9 THz. Finally, it is worth noting that this paper presents the first investigation of infrared spectra of Bi2-xCaxSn2O7-x/2 materials.

Is Cobalt Needed in Ni-Rich Positive Electrode Materials for Lithium Ion Batteries?

As a derivative of LiNiO2, NCA (LiNi1-x-yCoxAlyO2) is widely used in the electric vehicle industry because of its high energy density. It is thought that Co and Al both play important roles in enhancing NCA material properties. However, there is no solid evidence in the literature that clearly shows that Co is required in NCA with high nickel (e.g. when 1-x-y > 0.9) content. Therefore, a systematic study on the roles of different cation substituents in a series of LiNi1-nMnO2 (M = Al, Mn, Mg, or Co) materials was made. In-situ X-ray diffraction (XRD) and differential capacity versus voltage (dQ/dV vs. V) studies showed that the multiple phase transitions in LixNiO2 during charge and discharge, thought to cause poor charge-discharge capacity retention, were suppressed in LixNi0.95M0.05O2 (M = Al, Mn, or Mg), while 5% Co failed to suppress the phase transitions. First principles calculations were made to understand the function of each substituent. Accelerating rate calorimetry shows that unlike Al, Mn, or Mg, Co has no contribution to safety improvement. Therefore, we believe that Co brings little or no value at all to NCA-type materials with high Ni content (> 90% Ni in the transition metal layer) and we hope this paper will spur more interest in Co-free materials.