Stability of the LaCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> and LuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> Ions Studied by Mass Spectrometry

The enthalpy stability of the LaCl ₄ ^? and LuCl ₄ ^? ions is assessed using high-temperature mass spectrometry. The enthalpy of Cl^? detachment is determined to be Δ_rH⁰(298.15 K) = 332 ± 10 kJ/mol for LaCl ₄ ^? and 359 ± 10 kJ/mol for LuCl ₄ ^? .     

Estimating the effect of C<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and C<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> radicals and neutral clusters on the fullerene formation

The mass spectrum of the products of arc discharge in helium between graphite electrodes has been studied for various values of the gas flow rate. As the gas flow rate increases, the intensity of C₆₀^±, C₇₀^±, C₈₄^± and C₉₀^± fullerene peaks increases and that of the C₂⁻ and C₃⁺ cluster radicals decreases, but the total decay in radicals amounts to only 21% of the total growth of fullerenes. From this it follows that a contribution to the formation of fullerenes from the neutral clusters (which are taken into account for the first time) significantly exceeds the contribution due to small radical species.     

Formation-decomposition equilibrium of the NpO<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>·UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> complex in chloride melts

The absorption spectra of the NpO ₂ ⁺ (5f ²) ion were examined in the region of the 3H ₅ ← ³ H ₄ magnetic dipole transition (1530–1760 nm) for series of melts with the UO ₂ ²⁺ concentration varied in the opposite directions: (1) NaCl-2CsCl eutectic melt with growing additions of the Cs₂UO₂Cl₄ complex salt and (2) Cs₂UO₂Cl₄ melt with growing additions of the NaCl-2CsCl mixture. Measurements of the integrated intensities of the bands belonging to the NpO ₂ ⁺ ·UO ₂ ²⁺ complex and unbound NpO ₂ ⁺ throughout the UO ₂ ²⁺ concentration range examined (up to 4.4 M in neat Cs₂UO₂Cl₄ melt) and processing of the data obtained in terms of the mass action law showed that the formation-decomposition reaction of the cation-cation complex can be described adequately only using the equation of reaction in the form NpO₂Cl ₄ ^3? + UO₂Cl ₄ ^2? ? {Cl₄ONpO?UO₂Cl₃}^4? = Cl^? (with the equilibrium constant of 1.3±0.1). Thus, the formation of the cationcation complex should be treated as replacement of chloride ion in the equatorial plane of uranyl(VI) by neptunyl(V), rather than as simple addition of UO ₂ ²⁺ to NpO ₂ ⁺ . The reverse reaction, decomposition of the cation-cation complex, consists essentially in replacement of neptunyl(V) by chloride ion.     

Synthesis,electronic state,and particle size stabilization of nanoparticulate [Co(OH)<Subscript>2</Subscript>(H<Subscript>3</Subscript>O)<Stack><Subscript>δ</Subscript><Superscript>+</Superscript></Stack>]<Superscript>δ+</Superscript>

We have synthesized nanoparticulate cobalt(II) hydroxide containing Co²⁺ in tetrahedral oxygen coordination (Co _Td ²⁺ ), atypical of such systems: nano- [Co(OH)₂(H₃O) _δ ⁺ ]^δ+. The (Co _Td ²⁺ ) coordination in the hydroxide is inferred from its electronic diffuse reflectance spectrum, which shows a multiplet of strong absorption bands at 14500, 15000, and 16000 cm^?1 (⁴ A ₂(F)-⁴ T ₁(P) transition). Nanoparticulate cobalt(II) hydroxide forms in a weakly acidic medium under essentially nonequilibrium conditions due to supersaturation (by three to four orders of magnitude) with the starting reagents (CoCl₂ and LiOH) at the instant of the formation of the poorly soluble phase Co(OH)₂. Presumably, colloidal particles of nanoparticulate cobalt(II) hydroxide in a weakly acidic aqueous medium have a positive surface charge, compensated by a counter-ion (Cl^?) layer: nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ · δCl^?. The XRD patterns of pastes (gels) containing this hydroxide show three broad-ened lines with d = 5.31 (2θ = 16.7°), 2.77 (2θ = 32.3°), and 2.32 Å (2θ = 38.8°). According to small-angle X-ray scattering data, nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ has a narrow particle size distribution (1.0–2.0 nm). Synthesis and storage conditions are identified which ensure stabilization of the electronic state and particle size of nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ for a long time.     

Disproportionation of nonoxygenated U(V) bound in the complex with heteropoly anions P<Subscript>2</Subscript>W<Subscript>17</Subscript>O<Stack><Subscript>61</Subscript><Superscript>10−</Superscript></Stack>

The effect of experimental conditions on U^VL₂ (1–2 mM) disproportionation was studied spectrophotometrically through the U^IVL₂ accumulation (L = P₂W₁₇O ₆₁ ^10? ). In 1 M NaNO₃ solution containing 0.01 M HAc and 0.01 M NaAc, the rate of U^VL₂ disappearance is described by the equation V = k ₁[U^VL₂]. The k ₁ value is almost constant with pH decreasing from 4.5 to 1.7, but increases with increasing acetate concentration; the presence of 1 mM U^IVL₂, U(VI), or L does not affect k ₁. In the solutions of 0.1–1.0 M HClO₄ (ionic strength 1), the reaction rate is described by the equation V = 2k ₂[H⁺]^2.5[U^VL₂]². Probable disproportionation mechanism is discussed. The first stage is substitution of L by water molecules in the U^IVL₂ complex and appearance of the reactive U(V) complex with mixed coordination sphere.     

The reaction Pu(VI) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> ⇄ Pu(VII) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>4−</Superscript></Stack> in NaOH solutions

A spectrophotometric study showed that, in 5 M NaOH, Pu(VII) prepared by ozonation of Pu(VI) is reduced with excess K₄Fe(CN)₆. The Pu(VII) content can be estimated from the amount of the Fe(CN)₆³⁻ formed. In NaOH solutions of concentration exceeding 8 M, the Fe(CN)₆³⁻ ion oxidizes Pu(VI). In 10.3 M NaOH, the tenfold excess of K₃Fe(CN)₆ fully converts 1 mM Pu(VI) to the heptavalent state within 4 min (rate constant 1.3 l mol⁻¹ s⁻¹ at 20°C). With an increase in the NaOH concentration, the oxidation rate increases, and smaller excess of K₃Fe(CN)₆ is required. This oxidant is consumed not only for Pu(VI) oxidation but also in reactions with H₂O and OH⁻ ions. Pu(VII) is unstable and is slowly reduced with water and with products of decomposition of iron complexes.     

Stability of actinide(III,IV) and lanthanide(III,IV) complexes with P<Subscript>2</Subscript>W<Subscript>17</Subscript>O<Stack><Subscript>61</Subscript><Superscript>10−</Superscript></Stack> heteropolyanions

The total stability constants of Th⁴⁺, U⁴⁺, Np⁴⁺, Pu⁴⁺, Am⁴⁺, Cm⁴⁺, Ce⁴⁺, Tb⁴⁺, Pr⁴⁺, Tb³⁺, and Pr³⁺ complexes with P₂W₁₇O ₆₁ ^10? heteropolyanion in 1 M sodium salt solutions at pH ≥ 5.5 (i.e., when the anion is not protonated; so-called “absolute” constants), were determined experimentally or calculated from published data. Plots of constants vs. ionic radius of the f element were considered for solutions with ionic strength 1 (1 M acid or sodium salt solutions at pH ≥ 5.5). The correlations found confirm that the interaction of counterions in the complex is predominantly electrostatic. At the same time, different contributions of the covalent interaction for actinides and lanthanides were suggested.     

Excitation of the uranyl ion in oxidation of U(IV) with xenon difluoride in frozen aqueous solutions of sulfuric acid: IV. Effect of F<Superscript>−</Superscript> and UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> ions

A specific feature of U(IV) oxidation with xenon difluoride in aqueous H₂SO₄ solutions is low-temperature chemiluminescence (CL), which in the course of warming the sample quickly cooled to 77 K is recorded starting from 165 K and reaches a maximum at about 200 K. Exothermic phase transitions, crystallization of the ice + H₂SO₄·4H₂O and ice + H₂SO₄·6.5H₂O eutectics, occur in the same temperature range. The data (temperature dependences of the chemiluminescence intensity and simultaneously recorded DTA curves) obtained in experiments with variation of the rate of mixing and cooling the solutions and of the concentrations of H₂SO₄ and F^? and UO ₂ ²⁺ ions are well explicable by the catalytic activity of the juvenile surface of H₂SO₄ crystal hydrates toward low-temperature reaction of U(IV) with XeF₂.     

Synthesis,characterization and temperature studies on the conductivity of AlCl<Superscript>−</Superscript><Subscript>4</Subscript> ion doped polypyrrole

Synthesis of free standing conducting polypyrrole film using room temperature melt as the electrolyte is reported. We also report variation in the contribution of ionic conductance with temperature of the polymer film by four probe method and electrochemical properties like diffusion coefficient and ionic mobility of AlCl⁻₄ doped polypyrrole film. An attempt has been made to arrive at the stability of charge carrier concentration over a temperature range of 295 to 350 K under vacuum. The film was characterized by optical techniques and scanning electron micrography.     

Electrostatic self-assembly behaviour of exfoliated Sr<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>10</Subscript><Superscript>−</Superscript> nanosheets and cobalt porphyrins: exploration of non-noble electro-catalysts towards hydrazine hydrate oxidation

In our research, a convenient exfoliation/restacking route was used to fabricate a sandwich-structured nanocomposite of Sr₂Nb₃O₁₀/CoTMPyP [5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrinato cobalt] via electrostatic interaction between colloidal dispersion and cobalt porphyrin aqueous solution. The final self-assembled products were characterized by XRD, FTIR, UV–Vis, SEM, TEM, AFM, and ICP. During the exfoliation procedure, the well-dispersed Sr₂Nb₃O₁₀^? colloidal dispersion was obtained with the zeta potential value of ? 44.2 mV. Additionally, the existence of unilamellar Sr₂Nb₃O₁₀^? nanosheet was evidenced by AFM, and zeta potential values of the reassembly process with the addition of CoTMPyP aqueous solution into the colloidal dispersion were measured by a Zetasizer Nano apparatus. Above all, the final Sr₂Nb₃O₁₀/CoTMPyP hybrid film displayed excellent electro-catalytic activities towards hydrazine hydrate oxidation with peak potential at 0.158 V in pH 7.0 PBS indicated by CV measurements; moreover, a detection limit of 3.52 × 10^?5 M was obtained in the concentration range of 5 × 10^?5–9.9 × 10^?4 M at a signal-to-noise ratio of 3.0.     

Probe Mössbauer Spectroscopy of BiNi<Subscript>0.96</Subscript><Superscript>57</Superscript>Fe<Subscript>0.04</Subscript>O<Subscript>3</Subscript>

This paper presents results of a ⁵⁷Fe probe Mössbauer spectroscopy study of the BiNi_0.96⁵⁷Fe_0.04O₃ nickelate. The spectra measured above its TN demonstrate that Fe³⁺ cations heterovalently substitute for Ni²⁺ nickel (←Fe³⁺), being stabilized on four sites of the nickel sublattice in the structure of BiNiO₃. Calculations in an ionic model with allowance for monopole and dipole contributions to the electric field gradient indicate that the parameters of electric hyperfine interactions between ⁵⁷Fe probe atom nuclei reflect the specifics of the local environment of the nickel in the structure of the unsubstituted BiNiO₃ nickelate. Below T^N, Mössbauer spectra transform into a complex Zeeman structure, which is analyzed in terms of first-order perturbation theory with allowance for electric quadrupole interactions as a small perturbation of the Zeeman levels of the ⁵⁷Fe hyperfine structure, as well as for specific features of the magnetic ordering of the Ni²⁺ cations in the nickelate studied.     

Cathodoluminescence properties of SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript>and ZnO·SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript> phosphor nanopowders

The successful incorporation of ZnO nanoparticles in Pr³⁺-doped SiO₂ using a sol–gel process is reported. SiO₂:Pr³⁺ gels, with or without ZnO nanoparticles, were dried at room temperature and annealed at 600 °C. On the basis of the X-ray Diffraction (XRD) results, the SiO₂ was amorphous regardless of the incorporation of Pr³⁺ and nanocrystalline ZnO or annealing at 600 °C. The particles were mostly spherical and agglomerated as confirmed by Field Emission Scanning Electron Microscopy. Thermogravimetric analysis of dried gels performed in an N₂ atmosphere indicated that stable phases were formed at ≥900 °C. Absorption bands ascribed to ³H₄-³P_{(J = 0,1,2)}, ¹I₆ and ¹D₂ in the UV–VIS region were observed from SiO₂:Pr³⁺ colloids. The red cathodoluminescent (CL) emission corresponding to the ³P₀ → ³H₆ transition of Pr³⁺ was observed at 614 nm from dried and annealed SiO₂:Pr³⁺ powder samples. This emission was increased considerably when ZnO nanoparticles were incorporated. The CL intensity was measured at an accelerating voltage of 1-5 keV and a fixed beam current of 8.5 μA. The effects of accelerating voltage on the CL intensity and the CL degradation of SiO₂:Pr³⁺ and ZnO·SiO₂:Pr³⁺ were also investigated using Auger electron spectroscopy coupled with an Ocean Optics S2000 spectrometer.     

Synthesis and Structure of Mixed-Cation Salts with [PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the composition NaM₂[PuO₄(OH)₂]·4H₂O, where M = Rb (I) and Cs (III), and NaRb₅[PuO₄(OH)₂]₂·6H₂O (II) were synthesized and structurally characterized. The central Pu atom in [PuO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with oxygen atoms of hydroxide ions in apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb⁺ cations with 10- and 12-vertex coordination polyhedra (CPs), and in the structure of II, three independent Rb⁺ cations with the 12-, 11-, and 13-vertex CPs. In the structure of III, the Cs⁺ cation has a 12-vertex CP. Frameworks of large Rb⁺ or Cs⁺ cations can be distinguished in the structure. The CPs of the Pu and Na atoms (I, III) sharing a common edge or the isolated CPs of the Pu and Na atoms (II) are incorporated in these frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [PuO₄(OH)₂]^3– anions.     

Lewis and Brønsted acids in super-acid catalyst SO<Subscript>4</Subscript><Superscript>2−</Superscript>/ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>

Super-acid catalyst, SO₄ ^2?/ZrO₂–SiO₂, with high zirconium loading was synthesized and the nature of the surface acid was investigated by FT-IR of pyridine adsorption. With the increasing ZrO₂ content, the Lewis and Brønsted acid sites increased and reached the maximum when Zr/Si (molar ratio) = 1.3. The sample with Zr/Si = 1.3 showed the strongest IR adsorption band in the S=O stretching region (1,300–1,400 cm^?1). Pyrosulfate and monosulfate species existed on the surface of the catalysts and the acidic strength could be enhanced by induction effect of their S=O groups. And there were two kinds of Brønsted acid sites on the surface of the catalysts.     

Synthesis and Structure of Mixed-Cation Salts with [NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the general composition NaM₂[NpO₄(OH)₂]·4H₂O, where M = Rb (I, II) and Cs (III), were synthesized and structurally characterized. The compounds differ from each other in the structural organization. The Np central atom in [NpO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with the O atoms of hydroxide ions in the apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb cations with 10- and 12-vertex coordination polyhedra, and in the structures of II and III the framework of large cations is built of 12-vertex Rb and Cs polyhedra. The coordination polyhedra of the Np and Na atoms, sharing a common edge (I, III), or chains of the coordination polyhedra of the Np and Na atoms, sharing common vertices (II), are accommodated in the channels of the frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [NpO₄(OH)₂]^3– anions.     

Effect of salts on oxidation of Np(VI) with Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> Ions in 0.1–1 M alkali solutions

The potential of the Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ couple in solutions containing 0.5–1 M alkali and high concentrations of Li, Na, and K salts was estimated potentiometrically. The reactions of Fe(CN)₆³⁻ with Np(VI) in such media were studied by spectrophotometry. In 0.5–1 M KOH + 7 M KF or 0.5–1 M KOH + 8 solutions, Np(VI) is oxidized to the heptavalent state with a small excess of Fe(CN)₆³⁻. In the presence of lithium or sodium salts, a larger excess of the oxidant is required for complete oxidation of Np(VI). Carbonate ions in concentrations exceeding 2 M prevent the Np(VI) oxidation.     

Characterization of <Superscript>4</Superscript>I<Subscript>9/2</Subscript> ↔ <Superscript>4</Superscript>F<Subscript>3/2</Subscript> optical transitions in trivalent Nd<Superscript>3+</Superscript> ions in GaLaS glass

The positions of Stark levels have been determined, using a step-by-step procedure, in the ⁴I_9/2 and ⁴F_3/2 manifolds of Nd³⁺ ions from absorption and photoluminescence measurements in the 12–293 K temperature range. This data has been used to calculate the emission cross-section for which the maximum value turns out to be ～2.3 × 10^?20 cm². The radiative recombination time, calculated using Judd–Ofelt analysis, of the ⁴F_3/2 manifold is in close vicinity to the experimentally determined times that were measured by the conventional decay of PL after interruption of excitation and by QFRS. Moreover, the peak time defined by QFRS is independent of temperature. Therefore, the dominant relaxation mechanism from the ⁴F_3/2 excited manifold of Nd³⁺ ions in GaLaS glass is believed to be by radiative emission.     

Structure,electrical, and optical properties of ZnO-substituted PbO for the Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O glass system

Glasses of the 0.5Er³⁺/2.5Yb³⁺ co-doped (40Bi₂O₃–20GeO₂–(30 − x)PbO–xZnO–10Na₂O system where x = 0.0, 5, 10, 15, 20, 25, and 30 mol%) have been characterized by FT-IR spectroscopy measurements to obtain information about the influence of ZnO-substituted PbO on the local structure of the glass matrix. The density and the molar volume have been determined. The influences of the ZnO-substituted PbO on the structure of glasses have been discussed. The dc conductivity measured in the temperature range 475–700 K obeys Arrhenius law. The conductivity decreases while the activation energy for conduction increases with increase ZnO content. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400–1100 nm. The values of the optical band gap E _opt for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of dielectric constant have been determined.     

Synthesis and photoluminescence characterization of Ce<Superscript>3 + </Superscript> and Dy<Superscript>3 + </Superscript> activated ALa(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>(A = Na and Li) novel phosphors

In this paper, we report the synthesis of Ce^3 + and Dy^3 + activated alkali lanthanide tungstates, ALa(WO₄)₂(where A = Na and Li), prepared by solid state reaction method. The prepared phosphors were characterized by X-ray diffraction and photoluminescence techniques. The NaLa(WO₄)₂:Dy^3 + and LiLa(WO₄)₂:Dy^3 + phosphors show two emission peaks at around 574 and 486 nm (λ_exc = 354 nm). NaLa(WO₄)₂:Ce^3 + and LiLa(WO₄)₂:Ce^3 + show two emission peaks at around 378 and 425 nm (λ_exc = 350 nm). Excitation wavelengths of Ce^3 + and Dy^3 + activated alkali lanthanide tungstates are in near UV region i.e. Hg free excitation. These characterizations of phosphors are applicable for solid state lighting. Accordingly, Ce^3 + and Dy^3 + activated NaLa(WO₄)₂ and LiLa(WO₄)₂ may be the promising materials for solid state lighting applications.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.