Phase equilibria in the Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–CdO system and the thermal stability of Cd<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and CdNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Phase equilibria were studied in the Nb₂O₅–CdO system in the Nb₂O₅-rich region including CdNb₂O₆ and Cd₂Nb₂O₇. It was determined that CdNb₂O₆ and Cd₂Nb₂O₇ in air are stable to 1150 and 1120°C, respectively, and that, above these temperatures, there is solid-phase decomposition of niobates with CdO release in the gas phase. Along with the cadmium oxide evaporation, the Cd₂Nb₂O₇ decomposition is accompanied by the formation of cadmium metaniobate CdNb₂O₆ and the CdNb₂O₆ decomposition results in the formation of niobium oxide Nb₂O₅. No thermal events were observed in the differential thermal analysis curve for a 1: 1 CdNb₂O₆–Cd₂Nb₂O₇ mixture heated to 1100°C in air, which suggests that there are neither phase transformations in cadmium niobates, nor a eutectic within this temperature and concentration ranges. A study of the morphology of compacted samples of niobates determined specific conditions for producing dense composite ceramics, a mixture of niobates, that is suitable for using as a dielectric material.     

Synthesis and transport properties of perovskite-like phases (Sr,Ba)<Subscript>4</Subscript>E<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11 ± δ</Subscript> (E = Mn,Cr, Cu)

Synthesis of (Sr, Ba)₄Э₂Nb₂O_{11 ± δ} where E = Mn, Cr, Cu and solid solution (Sr_1?y Cu_y)_{6 ? 2x} Nb_{2 + 2x} O_{11 + 3x} is performed. By measuring the overall conductance of some solid-solution compositions it is established that the conductance increases with the cubic-lattice parameter and concentration of oxygen vacancies. Values of the conductance in humid air at T < 700°C are shown to increase as compared with dry air. Mass spectrometry analysis confirms the possibility of water incorporation into the complex-oxide structure out of a gas phase. Complex certification of samples of the composition (Sr, Ba)₄E₂Nb₂O₁₁ where E = Mn, Cr, Cu is performed. It is established that the decrease in the overall electroconductance occurs in the series Sr₄Mn₂Nb₂O₁₁ > Ba₄Mn₂Nb₂O₁₁ > Sr₄CrMnNb₂O₁₁ > Sr₄Cu₂Nb₂O₁₁. Investigation of the overall electroconductance in dry and moist atmospheres shows that the effect of humidity exerts no influence on the values of the overall electroconductance. The oxygen-ion constituent of conductance is determined by the Arzhannikov method and is also evaluated from a σ,pO₂ dependence. It is established that the presence of an element with a variable oxidation degree for compositions of the type Sr₄E₂Nb₂O₁₁ leads to an increase in the contribution made by the electronic constituent. In so doing, the magnitude of the oxygen-ion conductance practically does not alter. Thermal and mass spectrometry analyses show that, for the Sr₄E₂Nb₂O₁₁ compositions where E = Mn, Cr, Cu, there occurs no water intercalation into structure, correspondingly, there is observed no appearance of a protonic constituent of conduction.     

Phase equilibria,charge transport,and mass transport in Sr<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-“M<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>” (M = Cd,Cu, Ni,and Zn) systems

Homogeneous fields of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions were determined using powder X-ray diffraction. Phase fields were plotted proceeding from the tolerance factor t and electronegativity ratio $ \bar k_A /\bar k_B $ \bar k_A /\bar k_B with a satisfactory fit of experimental results. Thermogravimetry was used to establish the major kinetic laws of solid-phase synthesis (conversion, rate-controlling stage, and effective activation energy) in (4 − x)SrCO₃ + xMO + Nb₂O₅ powdery mixtures. Direct radiometry was used to determine ⁹⁰Sr, ⁶³Ni, and ⁶⁵Zn self-diffusion coefficients in solid solutions based on the Sr₄Nb₂O₉ phase. Electrical conductivity was measured as a function of temperature for all Sr₄Nb₂O₉-“M₄Nb₂O₉” samples. The conductivity of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions has a mixed ion-electron character.     

Phase formation in Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-K<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MMoO<Subscript>4</Subscript> (M = Ca,Pb, Ba) systems and the crystal structure of α-KLiMoO<Subscript>4</Subscript>

Solid-phase interactions in Li₂MoO₄-K₂MoO₄-MMoO₄ (M = Ca, Pb, Ba) systems were studied, and the subsolidus regions of these systems were triangulated. The lead and barium systems were studied in a more detailed way to discover that, along KLiMoO₄-K₂M(MoO₄)₂ (M = Pb, Ba), KLiMoO₄-PbMoO₄, and Li₂MoO₄-K₂Ba(MoO₄)₂ quasi-binary sections, there are homogeneity regions reaching 6–11 mol % based on K₂M(MoO₄)₂ and lead molybdate. Triple molybdates are formed in none of the systems, which is verified by experiments on spontaneous crystallization from solution in melt. Crystallization experiments yielded crystals of potassium dimolybdate and simple and double molybdates from the boundary systems. The crystal structure was solved for a hexagonal KLiMoO₄ phase: (Na,K){ZnPO4}, a = 18.8838(7) Å, c = 8.9911(6)Å, Z = 24, space group P6₃, R = 0.065. The structure comprises a three-dimensional tridymite framework built by an alternation of corner-sharing LiO₄- and MoO₄ tetrahedra wherein voids are occupied by potassium cations.     

A novel one-dimensional organic-inorganic polymer: synthesis and crystal structure of [{Ca(DMF)<Subscript>5</Subscript>}<Subscript>2</Subscript>SiMo<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Subscript>η</Subscript>

A novel polyoxometalate-based organic-inorganic polymer [Ca(DMF)_{5 2}SiMo₁₂O₄₀]_η has been synthesized and characterized by elemental analysis, IR, UV and X-ray single-crystal structural analysis. The title compound crystallizes in a monocline lattice, P2₁/n, with a =1. 3379 (3),b = 1. 9796 (4), c = 1. 4574 (3) nm, β= 92.24(3)δ,V= 3. 8568 (13) nm³, Z = 2,R ₁ = 0.083 andRw= 0. 2065. The result of crystal structure analysis indicates that Ca²⁺ is surrounded by seven coordination oxygen atoms with pentagonal bipyramidal geometry and bridged with terminal oxygen atom of polyanion in the structure. The compound contains an unprecedented one-dimensional linear chain built by alternate polyanions and cationic units through Mo-O_d-Ca-O-Ca links in crystal. The IR spectra and X-ray crystallography analysis exhibit that there is a strong interaction between the polyanion and organic group in solid state. The electronic spectra (λ= 200–500 nm) for the title compound dissolved in the mixed solvent of acetonitrile and water indicate that it is fully dissociated. The TGA/DTA study shows three stages of weight loss and that the thermal stability of polyanion is better than that of H₄SiMo₁₂O₄₀ · H₂O.     

Low temperature synthesis of Co<Subscript>2</Subscript>SiO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposite using a modified sol–gel method

The paper presents a study on the preparation of Co₂SiO₄/SiO₂ nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC₂H₅)₄), cobalt nitrate Co(NO₃)₂·6H₂O and some diols: ethylene glycol (C₂H₆O₂), 1,2propanediol (C₃H₈O₂) and 1,3propanediol (C₃H₈O₂), for a final composition: 30% CoO/70% SiO₂. During the heating of the gels at 140 °C, a redox reaction takes place between NO₃ ⁻ ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co₃O₄ inside the matrices pores. When CoO results, it reacts with SiO₂ at low temperature leading to Co₂SiO₄, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co₂SiO₄ (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM images, Co₂SiO₄ nanoparticles are homogenously dispersed inside the silica matrix.     

Liquid-phase synthesis and physicochemical properties of xerogels,nanopowders and thin films of the CeO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Low-agglomerated xerogels, ultrafine oxide powders with particle sizes of 12–20 nm, and uniform thin films with particle sizes of 8–14 nm are prepared in the CeO₂–Y₂O₃ system using liquid-phase low-temperature methods, namely via coprecipitation of hydroxides and cocrystallization of salts, sol—gel technology. A comparative characterization of the prepared xerogels and nanopowders is performed using a set of physicochemical analytical methods. A dependence of phase composition, microstructure, and particle size on synthetic parameters is elucidated.     

Multicomponent systems LiCl–LiBr–Li<Subscript>2</Subscript>SO<Subscript>4</Subscript> and LiCl–LiBr–Li<Subscript>2</Subscript>SO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>

Phase equilibria in the LiCl–LiBr–Li₂SO₄ ternary system and the LiCl–LiBr–Li₂SO₄–Li₂MoO₄ quaternary system were studied by differential thermal analysis. The compositions and temperatures of minima in the ternary and quaternary systems were determined to be (31.2 mol % LiCl, 46.8 mol % LiBr, 22.0 mol % Li₂SO₄, 460°C) and (25.2 mol % LiCl, 30.2 mol % LiBr, 14.6 mol % Li₂SO₄, 30.0 mol % Li₂MoO₄, 411°C), respectively.     

Distribution of niobium and lanthanum between two immiscible melts in the system LaPO<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–NaF–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The system LaPO₄–SiO₂–NaF–Nb₂O₅–Fe₂O₃ is characterized by immiscibility fields in the liquid state region. Addition of iron expands fields of immiscibility of melts and decreases the temperature of their coexistence. A fraction of 87–90% of niobium is extracted into iron silicate melt, and 92–98% of lanthanum is extracted into phosphate salt melt.     

Composition and Homogeneity of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>〈В〉 Solid Precursors and LiNbO<Subscript>3</Subscript>〈В〉 Batches

Nb₂O₅〈В〉 solid precursors and LiNbO₃〈В〉 batches prepared on their basis, which can be used for preparing optical-quality lithium niobate single crystals and pore-free piezoelectric ceramics, have been studied by laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The compositions of powdery samples pelletized without binder have been determined. The calculated mean-square deviations Sr of laser ablation ICP-MS have been used to show a homogeneous distribution of the boron dopant over Nb₂O₅〈В〉 precursors and LiNbO₃〈В〉 batches.     

Thermodynamic Properties of Zincate-Manganites of LaM<Subscript>2</Subscript> <Superscript>II</Superscript>ZnMnO<Subscript>6</Subscript> (М<Superscript>II</Superscript> = Mg,Ca, Sr,Ba) Composition

Temperature dependences of the heat capacity of new zincate-manganites of LaM₂^IIZnMnO₆ (M^II = Mg, Ca, Sr, Ba) composition are studied via experimental calorimetry in the interval of 298.15–673 K. It is found that all compounds have λ-shape effects on the curve of dependence C_p° ~ ?(T) with respect to phase transitions of the second kind. Equations for the temperature dependence of the heat capacity are derived with allowance for phase transition temperatures, and thermodynamic functions H°(T) ? H°(298.15), S°(T) and Φ^xx(T) are calculated on the basis of experimental data on C_p°(T) and the calculated S°(298.15) value.     

B<Subscript>2</Subscript>O<Subscript>3</Subscript> additives on sintering and microwave dielectric behaviors of Mg<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics synthesized through the aqueous sol–gel Process

The relationships between the sintering temperatures and the microwave dielectric properties of (1−x)Mg₄Nb₂O₉-xB₂O₃ (x = 0.5–10 wt. %) compounds were investigated by the sol–gel method in order to reduce the sintering temperature in this study. A suitable amount of B₂O₃ doping was effective in allowing low sintering temperatures without a little detrimental effect on these dielectric properties of the Mg₄Nb₂O₉ compounds. The variations in the dielectric constant (ε _r ) and the quality factor (Q·f) of the Mg₄Nb₂O₉ compounds depended on the amount of B₂O₃ doping and the sintering temperature. As a result, a ε _r value of ~12.8 and a Q·f value of ~142,570 GHz were obtained when the Mg₄Nb₂O₉ compound with x = 3% was sintered at 1,200 °C for 4 h. The temperature coefficient of resonant frequency (τ _f ) of the 3%-B₂O₃ doping Mg₄Nb₂O₉ compound slightly changed from −33 to −48 ppm/°C with an increased sintering temperature.     

Synthesis and thermal properties of Co<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> · 6H<Subscript>2</Subscript>O

The dependence of solid phase composition on the main parameters of the interaction in the CoSO₄-K₄P₂O₇-H₂O system was studied. The synthesis conditions were determined and a crystalline cobalt(II) diphosphat of the composition Co₂P₂O₇ · 6H₂O was synthesized. Its thermal properties were studied. The composition and the intervals, wherein the thermally stable products of partial and complete dehydration of Co₂P₂O₇ · 6H₂O are formed, were specified. The final heat treatment product, anhydrous α-Co₂P₂O₇, was identified and a sequence of the solid phase thermal transformations accompanying its formation was established.     

Electrophoretic sol–gel synthesis of SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> nanowires

We report the independent invention of perovskite ferroelectric nanowires strontium bismuth tantalate (SrBi₂Ta₂O₉, SBT). Electrophoretic sol–gel techniques have been used successfully. The morphology and structures are analyzed via SEM, TEM and XRD. SBT nanowires and nanoparticles filled template revealed 30 and 40 μm long, respectively. SBT are proved to be a single phase of orthorhombic perovskite structure. As it indicated, SBT nanowires has been crystallized at 700 °C. To minimize surface polarity, SBT nanowires oriented preferentially along the growing axis (c axis) by translation and rotation of atomic clusters of SBT.     

The synthesis and thermodynamic properties of strontium fluoromanganite Sr<Subscript>2.5</Subscript>Mn<Subscript>6</Subscript>O<Subscript>12.5 − δ</Subscript>F<Subscript>2</Subscript>

The existence of the [SrF_0.8O_0.1]_2.5[Mn₆O₁₂] = Sr_2.5Mn₆O_{12.5 ? δ}F₂ compound was established in the SrO-Mn₂O₃-SrF₂ system at 900°C and p(O₂) = 1 atm. The crystal structure of strontium fluoromanganite was determined from the X-ray powder diffraction data, electron diffraction, and high-resolution electron microscopy. It can be described in the monoclynic system with four Miller hklm indices: hklm: H = h a* + k b* + l c ₁ ^* + m q ₁, q ₁, q ₁ = c ₂ ^* = γc ₁ ^* , γ ≈ 0.632, a ≈ a ≈ 9.72 Å, b ≈ 9.55 Å, c ₁ ≈ 2.84 Å, c ₂ ≈ 4.49 Å, monoclinic angle γ ≈ 95.6°. The electromotive force method with a solid fluorine ion electrolyte was used to refine the composition of fluoromanganite and determine the thermodynamic functions of its formation from phases neighboring in the phase diagram (SrMn₃O₆, Mn₂O₃, SrF₂, and oxygen), ΔG°, kJ/mol = ?(111.7 ± 1.9) + (89.5 ± 1.5) × 10^?3 T.     

Sol–gel synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> nanocrystalline powder

Al₂O₃–TiO₂ nanocrystalline powders were synthesized by sol–gel process. Aluminum sec-butoxide and titanium isopropoxide chemicals were used as precursors and ethyl acetoacetate was used as chelating agent. Thermal and crystallization behaviors of the precursor powders were investigated by thermal gravimetric-differential thermal analysis, Fourier-transform infrared spectrum and X-ray diffraction. The average crystalline size of heat treated Al₂O₃–TiO₂ powders at 1,100 °C is ~100 nm.     

Low temperature and size controlled synthesis of monodispersed γ-Fe<Subscript>2</Subscript>O<Subscript>3 </Subscript>nanoparticles by an epoxide assisted sol–gel route

Monodispersed γ-Fe₂O₃ nanoparticles were prepared by a procedure-simple and precursor-cheap route, epoxide assisted sol–gel method. The γ-Fe₂O₃ nanoparticles were obtained by the reaction of FeCl₂ in ethanol solution with propylene oxide to form the sol, following by the boiling of the solution. As compared with other metal ions of +2 formal charge, the unexpected acidity of FeCl₂ in ethanol solution assure the formation of sol. As an advantage, the unique chemistry of this route results in the low temperature of synthesis, leading to the extremely small particle size of 2.3 nm and non-aggregation state of the particles.     

Thermal analysis study of LiFeO<Subscript>2</Subscript> formation from Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> mechanically activated reagents

Series of n-octadecane/expanded graphite composite phase-change materials (PCMs) with different mass ratio were prepared using n-octadecane as PCMs, expanded graphite as multi-porous supporting matrix through vacuum impregnation method. Microstructure, crystallization properties, energy storage behavior, thermal cycling property and intelligent temperature-control performance of the composite PCMs were investigated. Results show that the composite PCMs have a good energy storage property. The melting enthalpy and crystallization enthalpy can reach 164.85 and 176.51 J g^?1, respectively. Furthermore, the good thermal conductivity of expanded graphite reduces the super-cooling degree of n-octadecane and endows the composite PCMs with fast thermal response rate and excellent thermal cycling stability. As a result, the phase-change temperatures and phase-change enthalpy almost have no change after 50 thermal-cooling cycles. The test of intelligent temperature-control performance shows that the electronic radiator filled with the composite PCMs possesses a high intelligent temperature-control performance, and its temperature can sustain in the range of 22–27.5 °C for about 6120 s. These results indicate that the prepared composite PCMs possess good comprehensive property and can be widely used in energy storage and thermal management systems.     

The hydrothermal synthesis and crystal structure of [2.2′-bipyH]<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>

The title compound, [2.2′-bipyH]₃PW₁₂O₄₀, consists of three [2.2′-bipyH]⁺ and one Keggin structure heteropolyanion [PW₁₂O₄₀]^3?, which was hydrothermally synthesized and characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. It belongs to triclinic system, space group P \(\bar 1\), a = 12.086(3) Å, b = 12.777(4) Å, c = 19.152(4) Å, α = 88.861(2)Å, β = 89.851(3)Å, γ = 67.034(3)Å, M = 3345.72 g/mol, V = 2722.6(12) ų, Z = 2, D _c = 4.081 mg/m³, R₁ = 0.0474, wR ₂ = 0.1135, T = 293(2) K. In this compound, each of the three H⁺ ions locates at between the N atoms in one 2.2′-bipy molecule, respectively. The protonated cations and the heteropolyanion effect each other by the electrostatic force.