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.     

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.     

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 ^? .     

Chemical interaction of InAs,InSb, GaAs,and GaSb with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–C<Subscript>4</Subscript>H<Subscript>6</Subscript>O<Subscript>6</Subscript> etching solutions

This paper presents results on the kinetics and mechanism of the physicochemical interaction of InAs, InSb, GaAs, and GaSb semiconductor surfaces with (NH₄)₂Cr₂O₇–HBr–C₄H₆O₆ etching solutions under reproducible hydrodynamic conditions in the case of laminar etchant flow over a substrate. We have identified regions of polishing and nonpolishing solutions and evaluated the apparent activation energy of the process. The surface morphology of the crystals has been examined by microstructural analysis after chemical etching. The results demonstrate that the presence of C₄H₆O₆ in etchants helps to reduce the overall reaction rate and extend the region of polishing solutions.     

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.     

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.     

Chemical interaction of InAs,InSb, GaAs,and GaSb crystals with aqueous (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr solutions

We have studied the nature and kinetics of the chemical interaction of InAs, InSb, GaAs, and GaSb crystals with aqueous (NH₄)₂Cr₂O₇–HBr solutions. The dissolution rate of the crystals has been measured as a function of etchant composition, solution stirring rate, and temperature. The results demonstrate that the dissolution rate of the semiconductors is diffusion-limited. We have determined the composition ranges of polishing solutions, optimized their compositions, and found conditions for the dynamic chemical polishing of the semiconductors. Ultrasmooth polished semiconductor surfaces have been obtained, with R _a ≈ 1 nm.     

Synthesis of M(NpO<Subscript>4</Subscript>)<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (M = Mg,Ca, Sr,Ba) Using Н<Subscript>3</Subscript>ВО<Subscript>3</Subscript> Solutions and Properties of These Salts

Two procedures for preparing the compounds M(NpO₄)₂·nH₂O (M = Mg, Ca, Sr, Ba) using boric acid were suggested. In the first procedure, samples of freshly prepared salts M₃(NpO₅)₂·nH₂O (M = Ca, Sr, Ba) are treated with excess 0.5 M H₃BO₃ with vigorous stirring. In the process, the initially light green salts rapidly transform into black products of the general composition M(NpO₄)₂·nH₂O. In the second procedure, a measured volume of a Np(VII) solution with a known LiOH concentration was added to excess 0.5 M H3BO3 solution containing a calculated amount of Mg, Ca, Sr, or Ba nitrate. The reaction yields black precipitates of the same compounds as in the previous case. After washing with water and drying in an oxygen stream, the final products contain a small impurity of Np(VI). The IR spectra suggest that the compounds obtained are structurally related to the previously studied salts MNpO₄ (M = K–Cs), i.e., in their lattices there are neptunium–oxygen layers built of NpO₂³⁺ cations and bridging O atoms. New data on the properties of the compounds M₃(NpO₅)₂·nH₂O with M = Ca, Sr, and Ba were also obtained.     

Inter- and Intra-granular Interactions of REBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript>, RE: Eu,Gd, Ho and Er

Here, the superconducting and AC/DC magnetic properties of REBa₂Cu₃O_7−δ (RE: Eu, Gd, Ho and Er) are investigated in order to understand the inter-granular and intra-granular behavior of these compounds. These compounds were prepared by standard solid-state reaction route. ErBa₂Cu₃O_7−δ (Er-123) and HoBa₂Cu₃O_7−δ (Ho-123) (consisting of heavier rare earth) show higher orthorhombic splitting in their XRD patterns than those observed for EuBa₂Cu₃O_7−δ (Eu-123) and GdBa₂Cu₃O_7−δ (Gd-123) (consisting of lighter rare earth). Even though Eu, Gd, Ho and Er are magnetic elements, substitution of these at Y site in Y-123 does not change the superconducting transition temperature (T _c). Er-123 and Ho-123 exhibit very sharp superconducting transition while Eu-123 and Gd-123 exhibit relatively broad transition with little hump at the lower part of transition close to the long-range superconducting state with zero resistance. In addition to that, Eu-123 and Gd-123 show relatively higher normal state resistivity than those of Er-123 and Ho-123. The AC susceptibility measurements reveal that these compounds possess different strength of inter-granular couplings. The hump in the superconducting transition of Eu and Gd is not due to the lack of inter-grain couplings in these samples because of having better grain connectivity in the samples as compared to other rare earth elements in REBa₂Cu₃O_7−δ system. Though intra-grain peak is insensitive to the applied magnetic field, inter-grain peak is sensitive to the applied magnetic field.     

Structural,elastic, electronic,and optical properties of defect-chalcopyrite structure CdGa<Subscript>2</Subscript><Emphasis Type="Italic">X</Emphasis><Subscript>4</Subscript> (<Emphasis Type="Italic">X</Emphasis> = S,Se) compounds

First-principles calculations were performed to investigate the elastic, electronic, and optical properties of defect-chalcopyrite (DC) structure CdGa₂ X ₄ (X = S, Se) compounds. The present calculations shown that the DC structure CdGa₂ X ₄ (X = S, Se) compounds are mechanically stable and have similar electronic structures. Optical properties including the dielectric function, optical reflectivity, refractive index and electron energy loss, are discussed for radiation up to 22 eV, and present calculations reveal a weak anisotropy in CdGa₂S₄ and CdGa₂Se₄ compounds.     

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.     

Use of a nanostructured material for separation of <Superscript>238</Superscript>U and <Superscript>237</Superscript>U produced by the photonuclear reaction <Superscript>238</Superscript>U(γ, <Emphasis Type="Italic">n</Emphasis>)<Superscript>237</Superscript>U

²³⁷U was produced by the reaction ²³⁸U(γ, n) on an electron accelerator, MT-25 microtron, at the Flerov Laboratory of Nuclear Reactions. For the separation of ²³⁷U and [²³⁸U, the recoil nuclei were collected by a nanostructured material, hydrated manganese dioxide (of the cryptomelane type), in the solid-solid system. From fission products, ²³⁷U was separated by ion exchange. The specific activity of the resulting ²³⁷U was 4.5 × 10⁹ Bq (mg ²³⁸U)^-1, with the content of radioactive impurities of ≤10^-6 Bq Bq^-1. The chemical yield of ²³⁷U was 80%.     

Synthesis and study of structural,dielectric, magnetic and magnetoelectric properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–CoMn<Subscript>0.2</Subscript>Fe<Subscript>1.8</Subscript>O<Subscript>4</Subscript> composites

Magnetoelectric (ME) composites consisting of K_0.5Na_0.5NbO₃ (KNN) as ferroelectric phase and CoMn_0.2Fe_1.8O₄ (CMFO) as ferrite phase with general formula (x) CoMn_0.2Fe_1.8O₄–(1???x) K_0.5Na_0.5NbO₃ (x?=?10, 20, 30, 40 and 50 wt%) were synthesized using solid state reaction method. X-ray diffraction analysis asserts the existence of component phases including spinel phase of CMFO and orthorhombic phase of KNN. Field emission scanning electron microscopy has been used for studying the morphology and calculation of average grain size. The temperature dependent dielectric properties including dielectric constant (\(\varepsilon ^{\prime}\)) and dielectric loss (tan δ) at different frequencies has been studied and both are found to increase with incorporation of CMFO. Magnetic hysteresis loops have been measured at temperatures of 300 and 5 K. Variation of magnetization versus temperature has been studied in field cooled and zero field cooled modes. Polarization versus electric field (P–E) hysteresis loops are obtained at room temperature indicating presence of ferroelectric ordering in the composites at room temperature. The remnant polarization (2P_r) and coercive field (2E_c) are found to decrease linearly with incorporation of CMFO. ME voltage coefficient (α_ME) has been measured. The maximum value of α_ME is found to be 5.941 mV/cm-Oe for 10% CMFO–90% KNN bulk composite.     

Synthesis and magnetic properties of M<Subscript>0.08</Subscript>Ti<Subscript>0.91</Subscript>V<Subscript>0.09</Subscript>O<Subscript>2 + δ</Subscript> · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (M = Cr,Mn, Fe,Co, Ni) nanopowders

Using sol-gel synthesis and ion exchange, we have prepared titanium vanadium oxide nanopowders doped with transition-metal ions: M_0.08Ti_0.91V_0.09O_{2 + δ} · nH₂O with M = Cr, Mn, Fe, Co, and Ni. The valence state of the ions in the nanopowders and their morphology and structure have been studied by scanning electron microscopy, X-ray diffraction, IR spectroscopy, and X-ray photoelectron spectroscopy. The M _x Ti_0.91V_0.09O_{2 + δ} · nH₂O oxides dried in air or calcined at 400°C in air are shown to be paramagnets. Vacuum annealing of Co_0.08Ti_0.91V_0.09O_{2 + δ} · nH₂O at 700°C gives rise to a significant ferromagnetic contribution.     

Preparation,characterization, conductivity and thermal expansion studies of Ca<Subscript>0.5</Subscript>SbMP<Subscript>3</Subscript>O<Subscript>12</Subscript> (M = Al,Fe, Cr)

Nasicon type compounds of general formula Ca_0.5SbMP₃O₁₂ (M = Al, Fe, Cr) are prepared by solid-state method. All the compounds crystallize in hexagonal lattice with space group. The IR spectra show characteristic PO₄ vibrations. Conductivity studies indicate the presence of charged defects. The Cole-Cole plots of impedance are semicircles between 150 and 350 °C. The thermal expansion of these samples is studied in the temperature range 25–500 °C.     

Crystal structure of a Np(V) sesquioxalate,Na<Subscript>4</Subscript>(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

The crystal structure of a previously unknown Np(V) sesquioxalate, Na₄(NpO₂)₂(C₂O₄)₃·2H₂O was studied. The crystal structure consists of neptunyl(V) cations, sodium cations, oxalate anions, and water molecules of crystallization. Neptunyl(V) cations and oxalate ions form anionic chains [(NpO₂)₂(C₂O₄)₃] _n ^4n? . The coordination polyhedron (CP) of Np (pentagonal bipyramid) contains two apical “yl” oxygen atoms and five equatorial O atoms of three oxalate ions. The CP of Na(1) and Na(2) cations are combined through the common edges into zigzag chains in the [010] direction. Two independent oxalate ions are tridentate and tetradentate ligands.     

Synthesis and properties of Ca<Subscript>2.8</Subscript>Ln<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>O<Subscript>9 + δ</Subscript> (Ln = La,Nd, Sm,Tb-Er) solid solutions

Ca_2.8Ln_0.2Co₄O_{9 + δ} (Ln = La, Nd, Sm, Tb-Er) solid solutions have been prepared via a citrate route and their structural parameters have been determined. Their thermal expansion, thermoelectric power, thermal conductivity, and electrical conductivity have been measured above room temperature. The results demonstrate that all of the materials obtained are p-type semiconductors. Their unit-cell parameters decrease with a decrease in the ionic radius of the Ln³⁺ cation substituted for Ca²⁺, and their thermoelectric power increases with an increase in the number of f electrons of the Ln³⁺ cation. We have determined the electron and phonon contributions to the thermal conductivity of the materials and evaluated the thermoelectric power factor and thermoelectric figure of merit of the oxide ceramics. The highest thermoelectric power factors are offered by the Ca_2.8Tb_0.2Co₄O_{9 + δ} and Ca_2.8Er_0.2Co₄O_{9 + δ} solid solutions: 0.27 and 0.29 mW/(m K²), respectively, at T = 1100 K.     

Synthesis,microstructure, and electrical behavior of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> piezoelectric ceramics via a citric acid sol–gel method

Nanosize (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ precursor powders were prepared via the citric acid sol–gel method. The ceramics were sintered at 1100–1150 °C. All ceramics exhibit a single-phase perovskite structure. With increasing sintering temperature, the average size of grains in the samples changes slightly from 0.3 to 0.5 µm. All ceramics show obvious dielectric dispersion. Activation energy values were obtained via impedance, electric modulus, and conductivity, respectively, which are in the range of 0.60–1.06 eV. Compared to ceramics synthesized by solid-state reaction method, the as-synthesized samples are fine-grained and have high depolarization temperature and excellent temperature stability of the piezoelectric constant (d ₃₃). The d ₃₃ value of the sample sintered at 1120 °C remains as high as 119 pC N^?1 with increasing annealing temperature to 115 °C, whereas the reduced amplitude of d ₃₃ is only approximately 3%.     

Synthesis,structure and photocatalytic properties of <Emphasis Type="Italic">β</Emphasis>-ZrMo<Subscript>2</Subscript>O<Subscript>8</Subscript>

Monoclinic ZrMo₂O₈ was synthesized via solid state method and single crystals of the title compound have been grown by the hydrothermal method. The crystals belong to monoclinic crystal system with space group C2/c (No. 15) with a = 11·4243(19) Å, b = 7·9297(6) Å, c = 7·4610(14) Å and β = 122·15(2)°, Z = 4. The bandgap of the compound was 2·57 eV. Unlike the other polymorphs of ZrMo₂O₈, the monoclinic form has unique crystallographic features with ZrO₈ and Mo₂O₈ polyhedra. The photocatalytic activity of this compound has been investigated for the first time for the degradation of various dyes under UV irradiation and has been compared with the photoactivity of the trigonal form of ZrMo₂O₈. It has been observed that this compound exhibits specificity towards the degradation of cationic dyes.     

Glasses formation,characterization, and crystal-structure determination in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–TeO<Subscript>2</Subscript> system prepared in an air

A glass-forming domain is found and studied within Bi₂O₃–Sb₂O₃–TeO₂ system. The glasses composition were obtained in pseudo-binary xSbO_1.5, (1−x)TeO₂ for 0.05 ≤ x ≤ 0.20. The constitution of glasses in the system Sb₂O₃–TeO₂ was investigated by DSC, Raman, and Infrared spectroscopy. The influence of a gradual addition of the modifier oxides on the coordination geometry of tellurium atoms has been elucidated based Infrared and Raman studies and showed the transition of TeO₄, TeO₃₊₁, and TeO₃ units with increasing Sb₂O₃ content. XRD results reveal the presence of three crystalline: γ-TeO₂, α-TeO₂, and SbTe₃O₈ phases during the crystallization process. The density of glasses has been measured. The investigation in the ternary system by the solid state reaction using XRD reveals the existence of a solid solution Bi_1−x Sb_1−x Te_2x O₄ isotopic to BiSbO₄ with 0 ≤ x ≤ 0.1.