Isopolyoxorhenates observed by positive ion electrospray mass spectrometry

Unknown positive ion isopolyoxorhenates have been observed using electrospray ionization mass spectrometry (ESI+). The ESI+ studies of ammonium and alkali metal (Na⁺ and K⁺) perrhenate salts in aqueous solution at pH 4.5 show the existence of the series [A_x+1Re^VII_xO_4x]⁺ (where x=1–5 and A=NH₄⁺, Na⁺ and K⁺). In the potassium perrhenate system, the series [K_x+2Re^VRe^VII_xO_4x+3]⁺ (x=0–4) has also been characterised. All of these four series have {AReO₄} as the aggregation unit. In the ammonium perrhenate system, the monomeric Re(VII)-containing species, [(NH₄)₂(H₂ReO₅)]⁺, [(NH₄)₃(HReO₅)]⁺ and [(NH₄)₄(ReO₅)]⁺ were also detected.     

Electrochimie du polynitrure de soufre dans les solvants non aqueux—II. Comportement dans le carbonate de propylene

The electrochemical behaviour of polysulfur nitride and (SN)_x modified by bromine or lithium has been studied by cyclic voltametry in MClO₄, KPF₆, and MBr with M = Li⁺, Na⁺, K⁺, Et₄N⁺, propylene carbonate solutions. The cathodic reaction could produce (SN)_x alkaline insertion compounds. The buthyllithium chemical reaction could also give partially reversible (SN)_x alkaline insertion compounds.The products obtained could have the following formula: [SN(LiBu₄)_0.2]_x. Both compounds obtained by chemical and electrochemical reactions have similar electrochemical properties. A decomposition of the electrode material at a cathodic voltage of about ?2 V for the AgAg⁺ reference electrode occurred producing turquoise blue ions that could be oxidized to give a red coloration. (SN)_x bromine derivatives are the center of reversible oxido-reduction reaction in polysulfur nitride and its derivatives seem limited by the species diffusion in the solid.     

Synthesis optimization of Li1 + x[Mn0.45Co0.40Ni0.15]O2 with different spherical sizes via co-precipitation

Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂ spherical cathode materials with different sizes (about 2 and 5 μm) were fabricated by calcining uniform spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃ with lithium hydroxide at high temperature. The precursor of spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃, was obtained via co-precipitation method at room temperature, which was significantly dependent on synthetic conditions, such as the reaction temperature, the concentration of NH₄HCO₃, and stirring speed, etc. The optimized condition resulted in [Mn_0.45Co_0.40Ni_0.15]CO₃, of which the particle size distribution was uniform and the particle shape was spherical. The final products, Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂, had a well-ordered layered structure and uniform homogeneity. Raman spectroscopy analysis showed the Raman-active species E_g and A_1g modes were observed at 488, 473 cm^− 1 and 597, 590 cm^− 1, respectively, for the obtained spherical cathode materials.     

Structure versus relaxor properties in Aurivillius type compounds

Structure refinements in M^IIBi₄Ti₄O₁₅ (M^II = Ca, Ba), Bi_4−xBa_xTi_3−xNb_xO₁₂, (Na_0.5Bi_0.5)_1−xBa_xBi₄Ti₄O₁₅ and Bi₄Ti₃O₁₂–PbTiO₃ systems are used to report structural features of relaxor Aurivillius phases. In compounds with relaxor-like behaviour, the average structure is almost undistorted, closed to the archetypal HT paraelectric phase, with a tolerance factor ≳0.996. The coordination number of Bi³⁺ in fluorite layers changes from {4 + 2} for ferroelectrics to {4} for relaxors. Transmission Electron Microscopy reveals some characteristic features of relaxors such as micro-twinning, shearing-type defects which attest from the existence of a compositional inhomogeneity and a disorder at a local scale.     

Ordering structure of barium magnesium niobate ceramic with A-site substitution

The ordering behaviour of Ba(Mg_1/3Nb_2/3)O₃ ceramics (BMN) substituted by La³⁺, Na⁺, K⁺ was investigated using X-ray powder diffraction and transmission electron microscopy. The 1:2 ordered structure of BMN can be transformed to 1:1 ordered structure by substituting a small amount of La cation ion into the A-site. Moreover, the degree of ordering was increased with La content in the compound, and reached almost unity at [La] = 50 mol%. When the La ion in (Ba_1−xLa_x)(Mg_(1+x)/3Nb_(2−x)/3)O₃ (BLMN) was substituted by Na or K ions, the 1:1 ordered structure of BLMN was transformed into the 1:2 ordered structure. The degree of 1:2 ordering was influenced by the sintering temperature and the size difference between the A and B site ions.     

New isopolyoxovanadate ions identified by electrospray mass spectrometry

Ammonium metavanadate in aqueous solution at pH 4.5 displays in electrospray mass spectrometry experiments the presence of the two series of anions [H_xV_yO_z]⁻ (x=0, 1; y=1–9; z=3–23) and [H_xV_yO_z]²⁻ (x=0, 1; y=3–17; z=9–44) as well as [H₂VO₄]⁻, [V₁₀O₂₈]⁶⁻ and [H₅V₁₀O₂₈]⁻ ions. Further, the cation series [H_m+1(VO₃)_m]⁺ (m=1–6), [H_m−1V_mO_3m−1]⁺ (m=4–10) and [H_m−3V_mO_3m−2]⁺ (m=6–11) are observed. The series of protonated and unprotonated anions differ by {V₂O₅} units, the formal building block in these clusters. A range of polyoxovanadates not previously reported have been observed.     

Influence of Zr/Ti atomic ratio and seed layer on the magnetoelectric coupling of Pb(ZrxTi1−x)O3 film-on-CoFe2O4 bulk ceramic composites

Lead zirconate titanate Pb(Zr_xTi_1−x)O₃ films with various Zr/Ti ratios of 20/80, 40/60, 52/48, 60/40 and 80/20 are deposited on highly dense CoFe₂O₄ ceramics using a simple chemical solution deposition. All Pb(Zr_xTi_1−x)O₃ films are polycrystalline and have no preferential orientations. The dielectric, ferroelectric, piezoelectric and magnetoelectric properties strongly depend on the Zr/Ti ratio. And the Pb(Zr_xTi_1−x)O₃ films with a Zr/Ti ratio close to morphotropic phase boundary exhibit best properties, whose magnetoelectric coefficient is over 1.5 times larger than those of other Zr/Ti ratios. The introduction of a PbO seeding layer between the Pb(Zr_0.52Ti_0.48)O₃ films and CoFe₂O₄ substrates facilitates the (100)-texture. Therefore, the magnetoelectric coefficient was enhanced by 1.5 times. The further improvement of the magnetoelectric coupling could be anticipated by fabricating Pb(Zr_0.52Ti_0.48)O₃ films with more or absolute (100)-texture and using conductive interfacial layer between two phases.     

Defects characterization of Dy-doped BaTiO3 ceramics via electron paramagnetic resonance

The point defects and the structural and dielectric properties of Dy-doped BaTiO₃ ceramics prepared at 1400 °C were investigated. The solubility of Dy in the self-compensation mode was determined to be x = 0.07 for (Ba_1−xDy_x)(Ti_1−xDy_x)O₃, and no EPR signals associated with the Dy³⁺ Kramers ion or the Ba and Ti vacancies were detected using the electron paramagnetic resonance (EPR) technique. As x increases, the dielectric behavior changed from a first-order phase transition to a diffuse phase transition to a Y7R dielectric-temperature stability. A strong EPR signal at g = 1.974, which is rare among rare-earth-doped BaTiO₃ ceramics appeared unexpectedly in the single-phase (Ba_1−xDy_x)Ti_1−x/4O₃ ceramics with deliberately designed Ti vacancies. This signal was attributed to ionized Ba vacancy defects. A preference for the self-compensation mode of Dy³⁺ ions is responsible for the appearance of Ba vacancies. The real formula of the nominal (Ba_1−xDy_x)Ti_1−x/4O₃ is expressed as (Ba_1−xDy_3x/4)(Ti_1−x/4Dy_x/4)O₃. In addition, the defect chemistry is discussed.     

Structural and magnetic features of La0.7Sr0.3Mn1−xCoxO3 nano-catalysts for ethane combustion and CO oxidation

Structural, magnetic and catalytic properties of La_0.7Sr_0.3Mn_1−xCo_xO₃ (x=0.00, 0.25, 0.50, 0.75, 1.00) nano-perovskites prepared by the citrate method are investigated. The structural characterization of the compounds by X-ray powder diffraction and using X׳Pert package and Fullprof program is an evidence for a monoclinic structure (P21/n space group) with x=0.50 and a rhombohedral structure (R-3c space group) for other samples. These results have been confirmed by the FT-IR measurements. Crystallite size of the powders obtained from Halder–Wagner method has been compared with the Scherrer method. The structural and magnetic results suggest the presence of different concentrations of various cations of Co⁺², Co⁺³, Co⁺⁴, Mn⁺⁴ and Mn⁺³ in the samples. Activation energy, band gap energy, and electrical conductivity measurements have been employed to explain catalytic performance of the samples. The results of performance tests show that the sample with x=0.25 has the highest catalytic activity for CO oxidation, whereas, the sample with x=0.75 has the highest catalytic activity for C₂H₆ combustion.     

Unique Solubility of Switchable Alkyl-Amine Surfactants in Water

Because many amine surfactants are soluble in both water and CO₂ phases, they attract interest with regard to stabilizing CO₂-in-water dispersion systems. In our recent research, we find that the solubility of alkyl-amine surfactant in water can be significantly enhanced by salts, even though the salts are usually “salting-out” to other surfactants. The influence of various anions (NO₃⁻, Br⁻, Cl⁻, and SO₄²⁻) and cations (Na⁺, Ca²⁺, and Mg²⁺) on the alkyl-amine surfactants is investigated. The results are contrary to Hofmeister series and show that all the anions can enhance the solubility (salting-in) in the order of: NO₃⁻ > Br⁻ > Cl⁻ > SO₄²⁻, while the impact of the cations is insignificant. A physical–chemistry model based on the switchable property of the surfactant is proposed and well explains the experimental results. Therefore, the switchable alkyl-amine surfactants have potential to be applied under high-salinity and high-temperature conditions, for example, in enhanced oil recovery processes for a hot and salty carbonate reservoir.     

Synthesis and crystal structure solution of potassium dawsonite: An intermediate compound in the alkaline hydrolysis of calcium aluminate cements

Potassium dawsonite is formed as an intermediate compound during the alkaline hydrolysis (AH) in calcium aluminate cements (CACs). A synthesis method of potassium dawsonite has been developed. The crystal structure of potassium dawsonite KAl(CO₃)(OH)₂ has been solved by direct methods from X-ray powder diffraction data and refined with the Rietveld method. It crystallises in the orthorhombic Cmcm space group with unit cells parameters a=6.3021(3) Å, b=11.9626(5) Å, c=5.6456(3) Å and Z=4. The structure consists of carboaluminate chains, formed by the basic unit [Al₂(OH)₄(CO₃)₂]²⁻ arranged along the c axis. The carbonate groups are placed in an alternate manner at both sides of the carboaluminate chains. The carboaluminate chains are also held together by the K⁺ cations that are located in the middle of three such chains. Finally, the chemical reactions explaining the AH process in CACs are postulated.     

Evaluation of the electrochemical behavior and structural reversibility of Li3−xNaxV2(PO4)3/C (0≤x≤3) as anode materials for Na-ion batteries

A series of Li_3−xNa_xV₂(PO₄)₃/C (0≤x≤3) materials are successfully prepared by a simple solid-state reaction method and used for the first time as anode materials for Na-ion batteries. Powder X-ray diffraction (XRD) results show that the phase structures of Li_3−xNa_xV₂(PO₄)₃/C evolve along with the change of Li/Na atomic ratio (0≤x≤3). With increasing x in Li_3−xNa_xV₂(PO₄)₃/C from 0.0 to 3.0, the main phase in as-prepared sample transforms from monoclinic Li₃V₂(PO₄)₃ to rhombohedral Li₃V₂(PO₄)₃, and finally to rhombohedral Na₃V₂(PO₄)₃, which results in different sodium storage behavior and performance between Li_3−xNa_xV₂(PO₄)₃/C (0≤x≤3) materials. Electrochemical results show that Li_3−xNa_xV₂(PO₄)₃/C (x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0) can deliver the initial charge capacities of 21.1, 35.9, 33.8, 41.7, 43.3, 43.9 and 47.7 mAh g⁻¹ at a current density of 10 mA g⁻¹, respectively. After 45 cycles, the reversible capacities can be kept at 16.9, 45.1, 32.6, 44.6, 43.7, 37.8 and 27.3 mAh g⁻¹ for Li₃V₂(PO₄)₃/C, Li_2.5Na_0.5V₂(PO₄)₃/C, Li₂NaV₂(PO₄)₃/C, Li_1.5Na_1.5V₂(PO₄)₃/C, LiNa₂V₂(PO₄)₃/C, Li_0.5Na_2.5V₂(PO₄)₃/C and Na₃V₂(PO₄)₃/C, respectively. Furthermore, the structural reversibility of Li_3−xNa_xV₂(PO₄)₃/C (x=1.0, 2.0, and 3.0) is also observed by in-situ XRD observation during sodiation/de-sodiation process. All these observed evidences indicate that only some of Li_3−xNa_xV₂(PO₄)₃/C (0≤x≤3) can be used as possible sodium storage materials.     

Structural,electrical, dielectric and magnetic behavior of Gd1−xBixFe1−yZryO3 nanoparticles for advanced technological applications

Gd_1−xBi_xFe_1−yZr_yO₃ nanoparticles were synthesized via micro-emulsion route with different molar concentrations of Bi⁺³ (x) and Zr⁺⁴ (y). The values of x and y were kept in the range 0.00, 0.15, 0.30, 0.45 and 0.60. The characterizations were done by the thermo-gravimetric analysis (TGA), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The average particle size was ~50 nm. The effect of Bi³⁺ and Zr⁴⁺ contents on electrical, dielectric and magnetic parameters were studied. The DC resistivity measurements showed at certain Bi³⁺ and Zr⁴⁺ contents, more than two fold increase in electrical resistivity from 68×10⁸ Ω cm to 150×10⁸ Ω cm. The magnetic measurements showed the paramagnetic nature of Gd_1−xBi_xFe_1−yZr_yO₃ nanoparticles. The electrical and magnetic properties of these nanoparticles suggested that these materials are potential candidates for the fabrication of telecommunication and switching devices.     

New scheelite-type Cd1−3x⌷xGd2x(MoO4)1−3x(WO4)3x ceramics – their structure,thermal and magnetic properties

Polycrystalline samples of scheelite-type Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x solid solution with limited homogeneity (0<x≤0.25) and cationic vacancies (denoted as ⌷) have successfully prepared by a high-temperature annealing of CdMoO₄/Gd₂(WO₄)₃ mixtures composed of 50.00 mol% and less of gadolinium tungstate. Initial reactants and obtained ceramic materials were characterized by XRD, simultaneous DTA–TG, and SEM techniques. A phase diagram of the pseudobinary CdMoO₄–Gd₂(WO₄)₃ system was constructed. The eutectic point corresponds to 1404±5 K and ~70.00 mol% of gadolinium tungstate in an initial CdMoO₄/Gd₂(WO₄)₃ mixture. With decreasing of Gd³⁺ content in a CdMoO₄ framework, the melting point of Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x increases from 1406 (x=0.25) to 1419 K (x=0.0833), and next decreases to 1408 K (x=0). EPR method was used to identify paramagnetic Gd³⁺ centers in Cd_1−3x⌷_xGd_2x(MoO₄)_1−3x(WO₄)_3x for different values of x parameter as well as to select biphasic samples containing both Cd_0.25⌷_0.25Gd_0.50(MoO₄)_0.25(WO₄)_0.75 and Gd₂(WO₄)₃.     

Effect of site occupancies of rare earth ions on electrical properties in Ni-MLCC based on BaTiO3

The site occupancies of rare earth ions for Ba-site to Ti-site were quantitatively estimated in (Ba_1−x,R_x)(Ti_1−x,R_x)O₃ (R = Eu, Ho), (Ba_1−3xEu_2x)TiO₃, and Ba(Ti_1−2xEu_2x)O_3−x systems by applying the Rietveld refinement to the data obtained from the synchrotron radiation powder diffraction measurement. The occupational ratio of Ba-site to Ti-site for the larger rare earth ion (Eu) was 49/51 (x = 0.10), whereas for the smaller ion (Ho) was 9/91 (x = 0.01) in (Ba_1−x,R_x)(Ti_1−x,R_x)O₃ system. Furthermore, the occupational ratio was greatly dependent on the Ba/Ti ratio, in (Ba_1−3xEu_2x)TiO₃ system it was 92/8 (x = 0.03), whereas that in Ba(Ti_1−2xEu_2x)O_3−x system was 20/80 (x = 0.01). The Curie point shifted to lower temperature effectively with increasing in the occupational ratio of rare earth ion into Ba-site.     

The characterization of mixed titanate Ba1−xSrxTiO3 phase formation from oxalate coprecipitated precursor

Mixed titanates Ba_1−xSr_xTiO₃ were synthesized via calcination of oxalate coprecipitated precursors. On heating there were three thermal event occurred: T<250°C corresponds to the evaporation of trapped water and dehydration, T=250°C–450°C corresponds to the decomposition of oxalate and the formation of an intermediate phase where the composition is close to [Ba_1−xSr_x]₂Ti₂O₅.CO₃ and T=600°C–700°C corresponds to the carbonate decomposition and the formation of Ba_1−xSr_xTiO₃ phase. Powders calcined at T=700°C for 2 h are single phase, have grain size ranges of 0.2–2 μm and elongated morphology. Rietveld refinements of the XRD data showed single phase of perovskite structure in which their tetragonality decreased with increasing concentration of Sr²⁺ incorporated in Ba²⁺ site. The transition temperature showed strong correlation with the tetragonality.     

Synthesis and mechanism study of a dimeric tetranuclear carbonate-bridged copper(II) complex resulting from CO2 fixation by controlling O2 concentration

A dimeric tetranuclear carbonate-bridged Cu(II) complex [Cu₄(DPA-ⁱBu)₄(μ₂-CO₃)₂(MeOH)₂]^4 + 1 was prepared in-situ through oxidation of Cu(I) species by controlling the concentration of O₂ in CO₂. Lower concentration of O₂ led to the formation of 1 after CO₂ fixation but higher would give product as bis-μ₂-hydroxo complex [Cu(DPA-ⁱBu)(OH)]₂^2 + 2, which was found to be an intermediate to generate trinuclear carbonated complex [Cu₃(DPA-ⁱBu)₃(μ₃-CO₃)(MeCN)₂(H₂O)]^4 + 3. The mechanism of this reaction was proposed and the nucleophilic attack of μ-peroxo Cu(II) species to CO₂ molecules was suggested to be responsible for the generation of 1.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work, (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids, (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 1:2 [Zr(OBu ⁿ )₄:MAc] by FT-IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acid-butyric acid (PrCOOH)] was made for a combination ratio of 1:1:1 [MAc:RCOOH:Zr(OBu ⁿ )₄; R: Me, Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer coulometric titration and thermal analysis, respectively. Methyl ethyl ketone(MEK) and chloroform were chosen as solvents.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work; (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids. (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 1∶2 [Zr(OBu ⁿ )₄∶MAc] by FT IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acidbutyric acid (PrCOOH)] was made for a combination ratio of 1∶1∶1 [MAc∶RCOOH∶Zr(OBu ⁿ )₄∶R∶Me. Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV-spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer Coulometric titration and thermal analysis respectively. Methyl-ethyl-ketone (MEK) and chloroform were chosen as solvents.     

Ferroelectric properties of Li‐doped BaTiO3 ceramics

We prepared 3 kinds of Li⁺‐doped BaTiO₃ ceramics by the solid‐state reaction method: (i) (Ba_1?xLi_x)TiO_3?x/2 having A‐site Li⁺, (ii) Ba(Ti_1?xLi_x)O_3?3x/2 having B‐site Li⁺, and (iii) x/2 Li₂CO₃+BaTiO₃ mixed one, for which we investigated the stable site of Li. The density of all prepared ceramics is above 95%. The results show that the lattice structure, the grain size, and the electric properties of Li⁺‐doped BaTiO₃ ceramics are dependent on Li⁺ site. According to the increase in Li content, the cell volume of Ba_1?xLi_xTiO_3?x/2 decreases, but that of BaTi_1?xLi_xO_3?3x/2 increases. That of x/2Li₂CO₃+BaTiO₃ decreases by the small addition of Li, but increases by the large addition of Li. All Li⁺‐doped ceramics show antiferroelectric‐like double hysteresis loops. The shape of loops and the dielectric properties are also dependent on the Li site. We suggest that the role of oxygen vacancy accompanied by the Li‐doping is important. By comparison with the results of 3 type ceramics, it is concluded that at x/2Li₂CO₃+BaTiO₃ ceramics, the Li⁺ prefers to favorably substitute Ba²⁺ at A site for the low concentration of Li but its location was changed to Ti⁴⁺ site for the high concentration of Li.