Morphologies and properties of NiO particles prepared from NiSO<Subscript>4</Subscript>·6H<Subscript>2</Subscript>O and Ni(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O by spray pyrolysis

Nickel oxide particles were prepared by spray pyrolysis of aqueous solutions of NiSO₄·6H₂O and Ni(NO₃)₂·6H₂O. In spray pyrolysis reactor hollow salt particles initially formed were collapsed by decomposition to reduce their size. For NiSO₄·6H₂O less hollowness of the primitive particles and its higher decomposition temperature made the oxide particles highly spherical with very smooth surface. On the other hand the particles prepared from Ni(NO₃)₂·6H₂O were so hollow and fragile with rough surface since they were formed on the liquid pool of the salt melt. The particle size decreased with the furnace set temperature while increased with the initial salt concentration. Single oxide particle was composed of many small nuclei without sintering whose size varied with the rate of decomposition. The crystallinity of the particles increased with both temperature and the initial salt concentration. Preliminary drying in diffusion dryer fixed the size of the oxide particles from NiSO₄·6H₂O at that of the primitive particles, independent of the temperature. However, by the preliminary drying the particles from Ni(NO₃)₂·6H₂O became more hollow and fragile, whose sizes decreased with the temperature.     

Crystal Structure of Uranyl Malonate Trihydrate [UO<Subscript>2</Subscript>(OOC)<Subscript>2</Subscript>CH<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]·2H<Subscript>2</Subscript>O

Single crystals of [UO₂(OOC)₂CH₂(H₂O)]·2H₂O (I) were prepared by recrystallization of finely crystalline uranyl malonate trihydrate under hydrothermal conditions. The crystal structure of I consists of electroneutral [UO₂(OOC)₂CH₂(H₂O)]_n layers and water molecules located between them. The uranium coordination number is 7. The uranium coordination polyhedron is a distorted pentagonal bipyramid with the oxygen atoms of the uranyl group in the apices. The equatorial plane is occupied by four O atoms of three malonate ligands and the water molecule. The malonate anion is coordinated in the bidentate fashion to one uranyl ion to form a six-membered ring and in the monodentate fashion to two other uranyl ions.     

Synthesis of thorn-like Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>·H<Subscript>2</Subscript>O by hydrothermal method

Thorn-like polycrystalline Ca₂B₂O₅·H₂O microspheres with nano-sized slices were synthesized using boric acid and calcium hydroxide as reactants by a facile catalyst-free hydrothermal method at low temperature. The products were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern reveals that the Ca₂B₂O₅·H₂O is a monoclinic phase polycrystalline with cell parameters a = 0·6702, b = 0·5419 and c = 0·3558 nm. SEM also reveals that the monoclinic phase polycrystalline are thorn-like microspheres composed of many flakes with an average thickness of <100 nm. Possible reaction and growth mechanism were also discussed.     

Crystal structure of U(VI) phthalate dihydrate [UO<Subscript>2</Subscript>(OOC)<Subscript>2</Subscript>C<Subscript>6</Subscript>H<Subscript>4</Subscript>•H<Subscript>2</Subscript>O]•H<Subscript>2</Subscript>O

Crystalline uranyl phthalate dihydrate was prepared by hydrothermal method, and its crystal structure was determined. The crystal structure consists of infinite chains [UO₂LH₂O]_n coupled in bands [(UO₂)₂L₂(H₂O)₂]_n [L = C₆H₄(COO)₂], between which water molecules of crystallization are located. The coordination polyhedron of uranium atoms is a pentagonal bipyramid with the equatorial plane formed by oxygen atoms of three phthalate ions and coordinated water molecule. The U-O bond length in the UO ₂ ²⁺ cations is 1.766 . The coordination capacity of the ligands is 4. Anions are bidentately coordinated to uranium atoms to form seven-membered rings. Being bridging ligands, phthalate ions combine the neighboring uranium atoms into chains through one carboxy group, and the chains into bands, through the other carboxy group.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 513–515.Original Russian Text Copyright © 2004 by Charushnikova, Krot, Starikova.     

Low-frequency dielectric spectroscopy and electrical properties of Ca[B<Subscript>3</Subscript>O<Subscript>4</Subscript>(OH)<Subscript>3</Subscript>]·H<Subscript>2</Subscript>O single crystals near the phase transition

The dielectric properties and polarization of ferroelectric Ca[B₃O₄(OH)₃]·H₂O (colemanite) crystals are studied near the Curie temperature. The real part of dielectric permittivity (), dielectric losses (tan), pyroelectric coefficient (), and thermally stimulated depolarization currents are measured from -50 to 50°C. To assess the detailed nature of the phase transition (Curie temperature t_C~-7°C), the temperature dependences of and tan and are measured at frequencies f = 0.8-20 kHz. The results are used to determine () (where =f ) and (T) and evaluate the activation energy. The (t) data indicate that colemanite undergoes a diffuse phase transition.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1489–1494.Original Russian Text Copyright © 2004 by Slabkaya, Lotonov, Gavrilova.     

Thermodynamic properties of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> and Ho<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> in the range 10–340 K

The low-temperature heat capacity of Dy₂O₃ · 2ZrO₂ and Ho₂O₃ · 2ZrO₂ has been determined by adiabatic calorimetry in the temperature range 10–340 K. The results have been used to calculate the entropy, enthalpy increment, and reduced Gibbs energy of the zirconates without taking into account their low-temperature magnetic transformations.     

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 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.     

Synthesis,crystal structure,and properties of new actinide(VI) arsenates (H<Subscript>3</Subscript>O)[(AnO<Subscript>2</Subscript>)(AsO<Subscript>4</Subscript>)]·3H<Subscript>2</Subscript>O (An = U,Np, Pu)

Previously unknown arsenates of hexavalent U, Np, and Pu, (H₃O)[(UO₂)(AsO₄)]·3H₂O (I), (H₃O)· [(NpO₂)(AsO₄)]·3H₂O (II), and (H₃O)[(PuO₂)(AsO₄)]·3H₂O (III), were synthesized under hydrothermal conditions. The crystal structure of the compounds was determined, and their absorption spectra were measured. The compounds crystallize in tetragonal space group P4/nmm.     

High-temperature heat capacity of the oxide compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The compounds BiVO₄, Bi₄V₂O₁₁, and Bi₁₂V₂O₂₃ have been prepared by solid-state synthesis using stoichiometric mixtures of Bi₂O₃ and V₂O₅. The effect of temperature on the heat capacity of the synthesized bismuth vanadates has been studied by differential scanning calorimetry in the range 350–950 K. The C _p (T) curves have extrema at 531.7 K for BiVO₄ and at 725.2 and 852.8 K for Bi₄V₂O₁₁, which are due to polymorphic transformations of these compounds.     

Synthesis and vibrational properties of hematite (α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) nanoparticles

α- Fe₂O₃ nanoparticles have been synthesized by gel evaporation method in air at 300°C. The average size of as synthesized α-Fe₂O₃ nanoparticle was estimated to be 30 nm and the particles were of good crystalline nature. Shape of the nanoparticles were slightly deviated from spherical which is attributed to the asymmetric growth of primary nuclei. MicroRaman and X-ray diffraction results have shown mixed phases of α-Fe₂O₃ and γ-Fe₂O₃. However, the α-Fe₂O₃ phase is more predominant than γ-Fe₂O₃ due to the incomplete nucleation of α-Fe₂O₃ particles at the size of 30 nm. The vibrating sample magnetometer measurement shows that the nanoparticles possess ferromagnetic property.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.     

Structural investigation of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–K<Subscript>2</Subscript>O glass system with antibacterial potential

The xV₂O(1?x)[0.8 P₂O₅ ? 0.2 K₂O] glass system with 0 ≤ x ≤ 50 mol% was prepared and the structural changes induced in these glasses by increasing the vanadium oxide content were investigated by IR and ESR spectroscopies. The dual behaviour role of V₂O₅ oxide, as network modifier (for x ≤ 10 mol%) and the network former (x ≥ 20 mol%), as a consequence of phosphate network depolymerization and P–O–V and V–O–V linkages appearance was also highlighted. The antibacterial effect of the glasses with x ≤ 20 mol% V₂O₅ content was tested by optical density (OD) measurements. A linear correlation between the amount of vanadium and the antibacterial effect was evidenced.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Mechanical and acid-etching properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-containing ceramic fillers

The properties of the composite, having a complicated microstructure, are decided by many factors such as those of glass matrix, crystal phases, fillers, and holes. We investigated how the addition of ceramic fillers to the glass matrix affects the mechanical and etching properties of the glass composite by forming new crystal phases. Different amounts of two fillers, ZnO and Al₂O₃, were added to a glass frit consisting of Bi₂O₃–ZnO–B₂O₃. It was sintered at 550 °C for 30 min. Based on the results of this study, the porosity and degree of crystallization of the composites could be controlled by adjusting the content of the ZnO and Al₂O₃ fillers. Therefore, porosity and degree of crystallization formed by the reaction between a glass matrix and fillers influence the mechanical and etching properties of the composite.     

Effect of gamma radiation on electrical and optical properties of (TeO<Subscript>2</Subscript>)<Subscript>0·9</Subscript> (In<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0·1</Subscript> thin films

We have studied in detail the gamma radiation induced changes in the electrical properties of the (TeO₂)_0·9 (In₂O₃)_0·1 thin films of different thicknesses, prepared by thermal evaporation in vacuum. The current–voltage characteristics for the as-deposited and exposed thin films were analysed to obtain current versus dose plots at different applied voltages. These plots clearly show that the current increases quite linearly with the radiation dose over a wide range and that the range of doses is higher for the thicker films. Beyond certain dose (a quantity dependent on the film thickness), however, the current has been observed to decrease. In order to understand the dose dependence of the current, we analysed the optical absorption spectra for the as-deposited and exposed thin films to obtain the dose dependences of the optical bandgap and energy width of band tails of the localized states. The increase of the current with the gamma radiation dose may be attributed partly to the healing effect and partly to the lowering of the optical bandgap. Attempts are on to understand the decrease in the current at higher doses. Employing dose dependence of the current, some real-time gamma radiation dosimeters have been prepared, which have been found to possess sensitivity in the range 5–55 μGy/μA/cm². These values are far superior to any presently available real-time gamma radiation dosimeter.     

Crystal structure of a Pu(VII) potassium salt,K<Subscript>3</Subscript>PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O

A new Pu(VII) compound, K₃PuO₄(OH)₂·2H₂O, was synthesized, and its structure was studied by single crystal X-ray diffraction. This compound is isostructural to the previously described K₃NpO₄(OH)₂·2H₂O. The structure of the latter compound was redetermined to obtain more precise interatomic distances in the NpO₂(OH) ₂ ^3? anion. Changes in An-O bond lengths in the tetragon-bipyramidal coordination polyhedron of the compounds K₃AnO₄(OH)₂·2H₂O in going from Np(VII) to Pu(VII) were considered.     

Structure and properties of CaF<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

FTIR spectroscopy has been employed to investigate the structure of CaF₂–B₂O₃ glasses. It is proposed that CaF₂ partially modifies the borate network forming \textCa _{1 / 2} ²⁺ [\textBO _{3 / 2} \textF] ^- {\text{Ca}}_{ 1 / 2}^{ 2+ } [{\text{BO}}_{ 3 / 2} {\text{F]}}^{ - } units. The rest of CaF₂ is assumed to build an amorphous network formed of CaF₄ tetrahedra. Analysis of density and molar volume revealed that the volume of CaF₄ tetrahedron in the studied glasses is slightly greater than that in the crystalline form. Data of density, molar volume, and electric conductivity have been correlated with the glass structure. As far as the authors know, CaF₂–B₂O₃ glasses are investigated for the first time.     

Effect of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on microstructure,electrical properties,and aging behavior of ZnO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–MnO<Subscript>2</Subscript>–CoO varistor ceramics

The microstructure, electrical properties, and aging behavior of ZnO–V₂O₅–MnO₂–CoO–Dy₂O₃ varistor ceramics were investigated for different contents of Dy₂O₃. The microstructure consisted of ZnO grain as a main phase and secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, and DyVO₄. The average grain size increased from 7.6 to 10.1 μm and the sintered density slightly increased from 5.53 to 5.57 g/cm³ with the increase of Dy₂O₃ content. The varistor ceramics added with 0.05 mol% Dy₂O₃ exhibited the most nonlinear properties, with nonlinear coefficient of 30, and the highest stability against DC-accelerated aging stress. The Dy₂O₃ acted as an acceptor due to the decrease of donor density in the range of 2.73 × 10¹⁸/cm³ to 1.28 × 10¹⁸/cm³.     

Optical properties and crystallization of glasses in the system Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–MoO<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi₂O₃–MoO₃–B₂O₃. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The UV–Vis spectroscopy showed that the obtained glasses are transparent in the visible region. The values of optical band gap (E _opt) and changes in cut-off (λ_c) depending on composition are reported. It was established that the increase in the MoO₃ content led to decreasing the transmittance of the glasses. Moreover, the absorption edge shifts towards longer wavelength.