Novel In-based high entropy spinel oxides with tunable lattice parameter

A new set of high entropy oxides with spinel structure and variable number of constituents, from five to nine, was prepared keeping the cations in equimolar ratio or reflecting their tendency to occupy octahedral or tetrahedral sites. This approach increases the number of cations into a single phase, leading to larger configurational entropy and to an important unit cell expansion from ～8.28 to ～8.55 Å. Among the many cations used, In and Al played a significant role in controlling the lattice parameter, with In producing a relevant unit cell expansion and Al a cell contraction. We demonstrate for the first time the insertion of In into a single-phase high entropy spinel, where it occupies the tetrahedral site, compensated by the inversion of Ni²⁺ and other divalent cations. Finally, we estimated the cation distribution for each spinel to correlate the dependence of the spinel lattice parameter with the average ionic radius.     

In situ FTIR study of the decomposition of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ionic liquid during cathodic polarization of lithium and graphite electrodes

In this work we analyzed the cathodic reactions of an important ionic liquid (IL) based electrolyte solution, namely lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)/N-methyl-N-methylpyrrolidinium (BMP) TFSI. In situ FTIR spectroscopy was used for the analysis of gaseous products of the electrochemical decomposition of this IL solution during cathodic polarization of lithium metal and graphite electrodes. The main volatile product of the reductive decomposition of the anion in these BMPTFSI solutions is trifluoromethane. BMP cations decompose to mixtures of tertiary amines and hydrocarbons. The composition of the products is influenced by the nature of the anode material. Graphite possesses a catalytic activity in the electroreduction process of BMP cations which occurs along with their intercalation into the graphite structure. The liquid phase after cathodic polarization of graphite electrodes was analyzed by multinuclear NMR spectroscopy coupled with FTIR spectroscopy. ¹⁵N NMR and FTIR spectra revealed an increase in the Li cations content in the electrolyte solution, as a result of BMP cations decomposition during repeated cycling of graphite electrodes.     

Arene—onium cations—V. Preparative investigation concerning yields and selectivities for the anodic formation of some selected trisarene sulphonium cations

Based on kinetic data for the anodic oxidation of bisarenesulphonium cations[1] the preparative anodic oxidation of bisanisolesulphide, bisbenzenesulphide and bistoluenesulphide was performed in acetonitrile in presence of different arenes as coupling partners aiming to show that higher selectivities for the formation of desired trisarene sulphonium cations can be obtained provided appropriate process parameters are chosen. It is decisive to establish a concentration ratio {c(arene)/c(bisarenesulphide)} in the reaction layer which is high enough to keep the rate of anodic self-coupling vs the coupling with the desired arene low enough. For the formation of trisanisole sulphonium cations, where not self-coupling but coupling with water (yielding bisanisole oxide) is the most important competing reaction, a selectivity of 80% is already obtained if the ratio of the bulk concentrations of the competing coupling partners water and anisole is unity. In the case of the formation of tristoluenesulphide further advantage for obtaining a higher selectivity may be drawn from heterogeneous catalysis of the coupling reaction at carbon anodes. The yield for tristoluene sylphonium cations can be raised to nearly 90% at carbon anodes whereas oxidizing 0.1 M bistoluenesulphide in the presence of 0.1 M toluene at platinum anodes yields only undesired self-coupling products. From bisbenzenesulphide no trisbenzene sulphonium cations could be obtained; however, coupling with mesitylene, xylene and toluene was achieved.     

ESR-Spektroskopischer nachweis von radikalkationen bei der anodischen oxidation von alkylbenzolen in methylenchlorid und trifluoressigsäure

The anodic oxidation of hexaethyl- (HEB), hexa-methyl- (HMB), pentamethyl- (PMB) and 1,2,4,5-tetramethyl-benzene (TMB) on Pt in CH₂Cl₂ and CF₃COOH (TFA) is examined by cyclic voltammetry and esr spectroscopy. HEB, HMB and PMB are oxidized to the corresponding radical cations in TFA. The anodic oxidation of HMB and PMB in CH₂Cl₂ results in radical cations with one methyl group more than the starting material. The mechanism of the formation of these radical cations is discussed for HMB.     

In situ generation of diazonium cations in organic electrolyte for electrochemical modification of electrode surface

The modification of glassy carbon electrode was achieved by electrochemical reduction of in situ generated diazonium cations in acetonitrile. The in situ generation of 4-nitrophenyl diazonium cations in acetonitrile was investigated by spectroscopic methods. UV-visible spectroscopy revealed slow kinetics for the reaction of 4-nitroaniline with tert-butylnitrite in acetonitrile to form the corresponding diazonium cation. As a result, a coupling reaction, which implies a consumption of the amine and loss of the already formed diazonium cations, was evidenced by ¹H NMR spectroscopy. This spectroscopic study allowed the optimization of the in situ diazonium cations generation prior to the modification step. The electrochemical modification of the carbon electrodes with 4-nitrophenyl, 4-bromophenyl and anthraquinone groups was characterized by cyclic voltammetry and the resulting grafted layer were characterized by electrochemical techniques. The cyclic voltammetric behaviour during the electrochemical grafting was very similar to the one observed for an isolated diazonium salt dissolved in acetonitrile. In the case of the anthraquinone-modified electrode, the use of acetonitrile, into which the corresponding amine is soluble but not in aqueous media, allowed for its grafting by the in situ approach. The barrier properties of these grafted layers are similar to those obtained from isolated diazonium salts. Finally, the chemical composition of the grafted layers was determined by X-ray photoelectron spectroscopy and surface coverage in the range 5-7 × 10⁻¹⁰ mol cm⁻² was estimated for films grown in our experimental conditions.     

Understanding specific effects on the standard potential shifts of electrogenerated species in 1-butyl-3-methylimidazolium ionic liquids

It has been established that the dependence of the E° values in function of the electrochemical media selected for a large amount of reversible redox probes in reduction and also in oxidation. For such a purpose several electroactive substances either in reduction (4-nitrotoluene, 1,3-dinitrobenzene, tetrakis(dimethylamino)ethylene, 1,3,5-trinitrobenzene, and 2,4,6-trinitroanisole) or oxidation (ferrocene, tetrathiofulvalene, tris-4-bromophenylamine, tris-4-tolylamine, and N,N,N′,N′-tetramethyl-para-phenylenediamine) have been studied in aprotic RTILs based on unsymmetrical organic cations (quaternary ammonium cations, such as 1-butyl-3-methyl imidazolium) and a weakly coordinating inorganic anion (anions with low Lewis basicities, e.g., BF₄, PF₆). Ion-pairing effects between imidazolium ions and anions and dianions for the electrochemically generated species, the solvation differences between BF₄⁻/PF₆⁻ cations and dications as well as some different reaction mechanism pathways followed by these electrogenerated species in function of the solvent have also been carefully examined.     

A radical ion-pair complex exhibiting strong C–H…O H-bonding interaction,moderately broaden near-IR absorbance and complicated EPR spectrum

An ion-pair complex of [Ni(mnt)₂]^2? with p-N-benzylpyridinium α-nitronyl nitroxide radical cations (p-BzPYNN) in acetonitrile shows a moderate and broad absorbance in near-IR region. In the crystal of this complex, two radical cations form a dimer via strong H-bonding interaction; such kinds of dimers are connected into H-bonding chain by [Ni(mnt)₂]^2? dianions through weak H-bonding interactions. The neighboring H-bonding chains are arranged into supramolecular sheet via π…π stacking interactions between the five-membered chelate-ring of anion and the superimposed pyridyl rings of cations. The polycrystalline EPR spectrum exhibits two isotropic EPR signals. Based on the analyses of crystal structure, variable temperature magnetic susceptibility and electronic spectrum, the stronger EPR signal is assigned to the radical cation, the weaker one probably arises from a trace amount of [Ni(mnt)₂]^1? species.     

Enhancement of lignite char reactivity to steam by cation addition

Chars produced from lignites typically have much higher reactivities to gasification than those produced from bituminous coals. This has been attributed previously to the presence of carboxylate salts of inorganic constituents on the lignites. Upon charring of the lignites, the carboxylate salts decompose leaving behind well dispersed inorganic constituents which act as catalysts for gasification. In this study, a raw lignite has been treated with HCl and HF to demineralize it and to increase its carboxyl content prior to exchanging selected cations with the hydrogen on the carboxyl groups. Up to 2.14 mmol of calcium per g of coal could be added using this procedure. Addition of varying amounts of calcium to the lignite resulted in the production of chars containing calcium contents ranging from 1.1 to 12.9 wt %. Such addition resulted in a rectilinear increase in reactivity of the char to steam with increasing amount of calcium added. Maximum reactivity attained was over ten times the reactivity found for the char produced from the raw lignite. At comparable molar loadings of metal cations onto the acid-treated lignite, the chars subsequently produced had reactivities in steam in the order: K >Na ≈ Ca >Fe >Mg. Char reactivity could also be enhanced by the addition of cations to nitric acid-treated char which had been produced, in turn, from demineralized lignite.     

Electrochemiluminescence of rubrene at a zinc oxide electrode

The electrochemiluminescence (ecl of rubrene at a zinc oxide electrode has been studied with regard to the possibility of the formation of excited species via a heterogeneous electron-transfer reaction. Electrochemiluminescence has actually been observed, the spectrum of which coincides with the fluorescence spectrum of rubrene. However, the emitted light does not occur at potentials where rubrene radical cations are reduced but at potentials where radical anions are formed at the ZnO electrode. From this fact it is concluded that the emission observed originates from homogeneous electron transfer between radical cations and anions but not from formation of excited species via heterogeneous electron transfer. On the base of an energy diagram derived from the flat-band potential of ZnO in contact with a non-aqueous electrolyte and from electrochemical and photochemical data of rubrene the underlying processes are discussed qualitatively.     

Kinetics of phase transformations in SiAlON ceramics: I. effects of cation size,composition and temperature

Kinetics of direct α/β-Si₃N₄→α-SiAlON transformations, reverse α′-SiAlON→β′-SiAlON transformation, and the formation of intermediate phases were investigated for SiAlON ceramics with rare earth stabilizing cations. It was determined that smaller cations (Yb), and α-Si₃N₄ starting powders lead to faster Si₃N₄→α′-SiAlON transformations. Using the knowledge of phase stability of α′-SiAlON, these observations have been correlated to the overall driving force for the transformation, and the correlation is further extended to the reverse α′-SiAlON→β′-SiAlON transformation. Formation of intermediate phases during Si₃N₄→α′-SiAlON transformation is shown to depend on the α′-SiAlON formation and to be inversely correlated to the stability of α′-SiAlON. A thermodynamic interpretation thus emerges to account for the kinetics of SiAlON transformation that encompass the effects of the size of the stabilizing cations, type of starting powder, overall composition, and the reaction temperature.     

Perovskite structure and low frequency relaxor- like- dielectric response of (Sr,Ce)TiO3 solid solution

Phase composition, structure stability, cations valance state, and relaxor-like-dielectric behavior of Sr_(1–3/2x)Ce_xTiO₃ (SCT, x = 0.3, 0.4) solid solution were investigated systematically. The Sr_(1–3/2x)Ce_xTiO₃ samples appear to be single phase within the detection limits of the technique, whereas the solid solution exhibits the higher angle doublet and triplet peak splitting associated with (200) and (321). X-ray photoelectron spectroscopy (XPS) analysis showed that the Ce substitution induces change in the cations valance state upon oxygen vacancies formation. The system exhibits features of low-frequency dependent relaxor-like-dielectric behavior rather than sharp frequency-independent anomalies. Besides this, two kind of relaxations were detected in the temperature range ≥ 350 °C. According to the electric modulus and ac conductivity analysis, the relaxor-like-dielectric behavior results from the long-range conduction associated with ionized vacancies and mixed state of Ti^3+/4+ and Ce^3+/4+ cations.     

Nanocrystalline/nanosized manganese substituted nickel ferrites – Ni1−xMnxFe2O4 obtained by ceramic-mechanical milling route

Manganese substituted nickel ferrites, Ni_1−xMn_xFe₂O₄ (x=0, 0.3, 0.5 and 0.7) have been obtained by a combined method, heat treatment and subsequent mechanical milling. The samples were characterised by X-ray diffraction, differential scanning calorimetry and magnetic measurements. The increase of the Mn²⁺ cations amount into the spinel structure leads to a significant expansion of the cubic spinel structure lattice parameter. The crystallite size decreases with increasing milling time up to 120 min, more rapidly for the nickel–manganese ferrites with a large amount of Mn²⁺ cations (x=0.7). After only 15 min of milling the mean crystallites size is less than 25 nm for all synthesised ferrites. The Néel temperature decreases by increasing Mn²⁺ cation amount from 585 °C for x=0 up to 380 °C for x=0.7. The magnetisation of the ferrite increases by introducing more manganese cations into the spinel structure. The magnetisation of the milled samples decreases by increasing milling time for each ratio among Ni and Mn cations and tends to be difficult to saturate, a behaviour assigned to the spin canted effect.     

An effect of hydration entropy on adsorption of various alkylammonium ions at the mercury/water interface

The adsorption of various alkylammonium cations was investigated by measurement of the interfacial tension. Tetraethanolammonium ions (HOC₂H₄)₄N⁺ showed weaker adsorbability than that expected from its ionic radius. The adsorbabilities (relative surface excess of cation FΓ₊ and charge of specifically adsorbed cation q¹₊) of the ethyl series (C₂H₅)_nH_4?nN⁺(n = 0 ≈ 4), and of the methyl series (CH₃)_nH_4?nN⁺n = 0 ≈ 3) were directly proportional to the hydration enthalpies of these cations - ΔH⁰_h, but the proportionalities were different between the methyl and the ethyl series. A linear relation was, however, found between FΓ₊ and the hydration entropies - ΔS⁰_h without regard to the kinds of cations. A similar relation was also found between q¹₊? - ΔS⁰_h. In conclusion, the adsorbabilities of these cations were governed by the hydration entropy, not by the hydration enthalpy.     

Determination of the atmospheric precipitation pH value on the basis of the analysis of lichen cationoactive layer constitution

Studies of equilibria and kinetics of the ion exchange process between the surrounding (water solution) and lichens prove that the number of mobile hydrogen ions bonded in lichens depends on the concentration of hydrogen ions in the precipitation with which the lichens are in contact and the type and concentration of other cations contained in the precipitation. The measurement of these values was suggested; as a result, it enabled to determine the pH of precipitation by determination of mobile cations bonded in exposed or naturally grown lichens. The studies were conducted on Hypogymnia physodes lichens.     

Synthesis of fully and partially sulfonated polyanilines derived from ortanilic acid: An electrochemical and electromicrogravimetric study

The electrochemical polymerization of 2-aminobenzene sulfonic acid, also called ortanilic acid (o-ASA), on a gold electrode precoated with polyaniline (PANI), has been carried out. We proved that the electropolymerization of o-ASA is enhanced on PANI electrodes, resulting in thicker films obtained in aqueous media at room temperature. The electrosynthesized film (P(o-ASA)) was characterized by cyclic voltammetry, FTIR and nuclear magnetic resonance. The compensation of P(o-ASA) charge was evaluated using electrochemical quartz crystal microbalance combined with cyclic voltammetry, which showed that the electroneutralization process mainly involves cations. Additionally, copolymers of aniline and o-ASA were electrosynthesized, using a metallic electrode modified with PANI also as a working electrode. The degree of sulfanation of copolymers has been modulated with the proportions of monomers in the electrosynthesis solution. The studies reveal a more important participation of cations in fully sulfonated polyaniline than in partially sulfonated polyaniline.     

Combined analysis of self-diffusion, conductivity, and viscosity data on room temperature ionic liquids

The self-diffusion coefficient of anions and cations, the ionic conductivity and the viscosity of four room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), 1-butylpyridinium tetrafluoroborate (BPBF₄), and 1-butylpyridinium bis(trifluoromethylsulfonyl)imide (BPTFSI) were analysed within a comprehensive ionic transport model. The experimental data, covering wide temperature ranges, were taken from the work of Noda et al. [J. Phys. Chem. B, 105, 2001]. To compare the dc conductivity with the self-diffusion coefficients, the former quantity was converted into a charge diffusivity D_σ using the Nernst-Einstein equation. In a similar way, we calculated a viscosity-related diffusivity D_η with the aid of the Stokes-Einstein equation. Taking three mobile species into account, i.e., single cations, single anions and neutral ion pairs, our model yields their individual diffusivities that obey a uniform Vogel-Tammann-Fulcher-like temperature dependence described by common values of the parameters B and T₀. Evaluating simultaneously all experimental data within this model yields the contribution of ion pairs to the self-diffusion coefficient of cations and anions separately. We further obtain the temperature-independent cation transference number and the effective hydrodynamic radius, which are important characteristics of charge and mass transport in these ionic liquids.     

Specific adsorption of tetra-alkyl ammonium iodide at the mercury—solution interface and the influence of the double-layer structure on the kinetics of zinc ions

The effect of adsorption of tetra-alkyl ammonium iodide at the dme has been examined with Faradaic impedance measurements. The differential capacitance of mercury in the salt solutions of the type R₄NI, where R is CH₃, C₂H₅ and n-C₃H₇ at 25°C as a function of polarization is measured. The parameters of the electrocapillary maximum, E_max and σ_max, are evaluated. By comparing the differential capacitance curves with those observed in other aqueous salt solutions of the same concentration and assumed to exhibit specific adsorption, it is shown that the cation is specifically adsorbed and that adsorption increases from tetra-methyl to tetra-ethyl to tetra-propyl salts. On the anodic limb of the capacity curve it is assumed that there is simultaneous specific adsorption of cations and anions. The anions thus form bridges between the cations and the mercury surface. The apparent standard rate constant K_s for the discharge of Zn(II)/Zn(Hg) in 1 M NaClO₄ was found to decrease in the presence of the quaternary cations and accelerated by iodide only. This phenomena is similar to that observed with the hydrogen evolution reaction at the mercury electrode and is opposite of those observed with anions of the persulphate type.     

Structural and magnetic evaluation of substituted NiZnFe2O4 particles synthesized by conventional sol–gel method

The aim of this study is to evaluate the structural and magnetic properties of Ni–Zn doped ferrite with trivalent Al³⁺ and Cr³⁺ cations substitution in Ni_0.6Zn_0.4Fe_2−xCr_x/2Al_x/2O₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) synthesized by employing conventional sol–gel method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), Mössbauer spectroscopy (MS) and vibrating sample magnetometer (VSM) analysis were carried out in order to characterize the structural and magnetic properties of particles. The XRD results confirmed the formation of single phase of spinel ferrite particles for a whole series of samples. The results of FTIR analysis indicated that the functional groups of Ni–Zn spinel ferrite were formed during the sol–gel process. Furthermore, FE-SEM micrographs revealed that the distribution of particles size is narrow. According to Mössbauer spectra,the doped cations are replaced in iron site occupancy of octahedral sites. It was found that with an increase in substitution contents magnetization decreased due to occupation of Al and Cr cations at low level substitutions in octahedral sites.     

Deformation behaviour of iron-doped alumina

Compressive creep tests in air were carried out on 1 cat.% Fe-doped alumina at a temperature T=1400 °C. Iron doping affected the plastic deformation by different ways in relation with Fe²⁺ cations population. Fe²⁺ cations sped up the deformation rates. FeAl₂O₄ spinel precipitates were identified and they were found (i) to interact with alumina grain boundaries (ii) to limit the grain growth within a range of strain. The Fe²⁺ cations underwent oxidation and this resulted in the dissolution of the some precipitates and in the decrease of deformation rates. It was suggested that deformation sped up this evolution through mass transport and that time was not a dominating parameter.