New Phosphate-Sulfates with NZP Structure

NaZr_2–xB_x(PO₄)_3–2x(SO₄)_2x (0 ≤ x ≤ 1.25, B = Mg, Co, Ni, Cu, Zn), and NaZr_2–xR_x(PO₄)_3–x(SO₄)_x (0 ≤ x ≤ 1.25, R = Al, Fe) phosphate-sulfates series have been prepared by a sol–gel process. These compounds belong to the NaZr₂(PO₄)₃ (NZP) structure family and crystallize in hexagonal crystal system, space group R\(\bar 3\)c. Limited solid solution series were found to exist; their formation temperatures and thermal stability limits were determined. Particle sizes as determined by microstructure observation were 50–200 nm, and for Cu- and Zn-containing samples, 200–500 nm. The thermal expansion of phosphate-sulfate NaZr_1.25Cu_0.75(PO₄)_1.5(SO₄)_1.5 was studied in the range 25–700°C. Thermal expansion coefficients and thermal expansion anisotropy were found to be α_a =–5.40 × 10^–6 °C^–1, α_с = 18.88 × 10^–6 °C^–1, α_avg = 2.69 × 10^–6 °C^–1, and Δα = 24.28 × 10^–6 °C^–1.     

Isomorphic substitution of neodymium and gadolinium for calcium in synthetic hydroxovanadate

Isomorphic substitution of neodymium and gadolinium for calcium in synthetic hydroxovanadate Ca_{5 ? x} M _x (VO₄)₃(OH)_{1 ? x} O _x (M = Nd, Gd) is studied in the range 700–1000°C using X-ray powder diffraction, single-crystal X-ray diffraction (Rietveld technique), and IR spectroscopy. Single-phase solid solutions at 800°C are formed with x ≤ 0.35 for M(III) = Nd and x ≤ 0.3 for M(III) = Gd. With high x, the apatite solid solution coexists with Ca₃(VO₄)₂, Nd₂O₃, and X phases. With increasing x in the homogeneous region, the intensity of the bands of stretching vibrations and librations of OH groups decrease. Single-crystal X-ray diffraction shows that neodymium and gadolinium substitute for calcium in solid solutions mostly in Ca(2) positions.     

Synthesis,structure, and thermal expansion of sodium zirconium arsenate phosphates

Sodium zirconium arsenate phosphates NaZr₂(AsO₄) _x (PO₄)_3?x were synthesized by precipitation technique and studied by X-ray diffraction and IR spectroscopy. In the series of NaZr₂(AsO₄) _x (PO₄)_3?x , continuous substitution solid solutions are formed (0 ≤ x ≤ 3) with the mineral kosnarite structure. The crystal structure of NaZr₂(AsO₄)_1.5(PO₄)_1.5 was refined by full-profile analysis: space group R \(\bar 3\) c, a = 8.9600(4)Å, c = 22.9770(9) Å, V = 1597.5(1) ų, R _wp = 4.55. The thermal expansion of the arsenate-phosphate NaZr₂(AsO₄)_1.5(PO₄)_1.5 and the arsenate NaZr₂(AsO₄)₃ was studied by thermal X-ray diffraction in the temperature range of 20–800°C. The average linear thermal expansion coefficients (α_av = 2.45 × 10^?6 and 3.91 × 10^?6 K^?1, respectively) indicate that these salts are medium expansion compounds.     

Phase equilibria in systems of gallium sulfate with lithium or sodium sulfate

The phase diagrams of binary systems of gallium sulfate with lithium or sodium sulfate were studied for the first time. The Li₂SO₄–Ga₂(SO₄)₃ system is of the eutectic type. The coordinates of the eutectic are (548°C, 30 mol % Ga₂(SO₄)₃). The region of a solid solution based on the high-temperature modification α-Li₂SO₄ is small. In the Na₂SO₄–Ga₂(SO₄)₃ system, compound Na₃Ga(SO₄)₃ forms, which melts incongruently at 585°C. The coordinates of the eutectic are (538°C, 17 mol % Ga₂(SO₄)₃). The region of a solid solution based on α-Na₂SO₄ reaches 8 ± 1 mol % Ga₂(SO₄)₃. The X-ray powder diffraction pattern of Na₃Ga(SO₄)₃ was indexed in a tetragonal unit cell with the parameters a = 9.451(3) Å and c = 7.097(3) Å; the unit cell parameters for an aluminum-containing analog, Na₃Al(SO₄)₃, are a = 9.424(5) Å and c = 7.053(3) Å.     

Substitution of barium for strontium in hydroxovanadate structure

A possibility of substitution of barium for strontium in Sr₁₀(VO₄)₆(OH)₂ is studied by X-ray powder diffraction and IR spectroscopy. According to X-ray powder diffraction data, single-phase solid solutions Sr_{10 ? x} Ba _x (VO₄)₆(OH)₂ are formed with x = 0–2.5 with an increase in the unit cell parameters.     

Formation of mononuclear rhodium(III) sulfates: <Superscript>103</Superscript>Rh and <Superscript>17</Superscript>O NMR study

It was shown that the monomeric rhodium sulfate complexes [Rh(H₂O)₄(SO₄)]⁺, trans-[Rh(H₂O)₂(SO₄)₂]^?, cis-[Rh(H₂O)₂(SO₄)₂]^?, and [Rh(SO₄)₃]^3? were not predominant forms in aqueous solutions. The ¹⁰³Rh NMR chemical shifts of the complexes were assigned, and the conditions for their formation in solutions, concentration parameters, and acidity at which the fraction of the monomers was maximal were determined. The constants of formation of the complexes and ion pair (IP) were estimated: K _IP = 8 ± 3.5, K ₁ ≈ 8, K _2trans ≈ 1, K _2cis ≈ 1, and K ₃ ≈ 2.     

Effects of Cr doping on the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

A series of Cr-doped Li₃V_2???x Cr _x (PO₄)₃ (x?=?0, 0.1, 0.25, and 0.5) samples are prepared by a sol–gel method. The effects of Cr doping on the physical and chemical characteristics of Li₃V₂(PO₄)₃ are investigated. Compared with the XRD pattern of the undoped sample, the XRD patterns of the Cr-doped samples have no extra reflections, which indicates that Cr enters the structure of Li₃V₂(PO₄)₃. As indicated by the charge–discharge measurements, the Cr-doped Li₃V_2???x Cr _x (PO₄)₃ (x?=?0.1, 0.25, and 0.5) samples exhibit lower initial capacities than the undoped sample at the 0.2 C rate. However, both the discharge capacity and cycling performance at high rates (e.g., 1 and 2 C) are enhanced with proper amount of Cr doping (x?=?0.1). The highest discharge capacity and capacity retention at the rates of 1 and 2 C are obtained for Li₃V_1.9Cr_0.1(PO₄)₃. The improvement of the electrochemical performance can be attributed to the higher crystal stability and smaller particle size induced by Cr doping.     

A study of phase formation in the subsolidus region of the system Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MnMoO<Subscript>4</Subscript>-Cr<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phase relationships in the subsolidus region of the system Na₂MoO₄-MnMoO₄-Cr₂(MoO₄)₃ were studied by means of X-ray diffraction and differential-thermal analyses. The possibility of obtaining a variablecomposition phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ (0 ≤ x ≤ 0.5) and ternary molybdate NaMn₃Cr(MoO₄)₅ was examined. The temperature dependence of the conductivity of the phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ was analyzed.     

Methanol transformations on framework lithium zirconium vanadate phosphates

The catalytic activity of framework phosphates of the general formula LiZr₂(VO₄)_x(PO₄)_3–x with different degrees of phosphorus replacement (x = 0, 0.1, 0.3, 0.4, 0.6, and 0.8) was studied in methanol transformations in an inert atmosphere. It was shown that the ratio between the activity and selectivity of the catalysts in dehydration and dehydrogenation reactions is determined by their vanadium content and the process temperature.     

Phase formation in the Ag<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MgMoO<Subscript>4</Subscript>-Al<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> system

The subsolidus region of the Ag₂MoO₄-MgMoO₄-Al₂(MoO₄)₃ ternary salt system has been studied by X-ray phase analysis. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgMg₃Al(MoO₄)₅ has been determined. The Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ variable-composition phase is related to the NASICON type structure (space group R \(\bar 3\) c). AgMg₃Al(MoO₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P \(\bar 1\), Z = 2) with the following unit cell parameters: a = 9.295(7) Å, b = 17.619(2) Å, c = 6.8570(7) Å, α = 87.420(9)°, β = 101.109(9)°, γ = 91.847(9)°. The compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ and AgMg₃Al(MoO₄)₅ are thermally stable up to 790 and 820°C, respectively.     

Electron transport properties of thermoelectrics based on layered substituted transition metal dichalcogenides

Temperature dependences of the electrical conductivity are studied in the range 4.2’300 K and Seebeck coefficient at room temperature of bulk samples of tungsten dichalcogenide polycrystals with niobium substitutions for tungsten and selenium substitutions for sulfur – W_1–x Nb _x (S_1–y Se _y )₂. The two-dimensionalization of electron transport properties is detected at niobium concentrations x ≥ 0.1 in W_1–x Nb _x S₂ and x ≥ 0.05 in W_1–x Nb _x Se₂. In samples with additional partial selenium substitution for sulfur the electron transport remains three-dimensional. At room temperature the Seebeck coefficient (at equal electrical conductivities) is several times higher in the samples with quasi-two-dimensional transport than in the samples with three-dimensional transport. The calculation of the power factor at room temperature shows its nine times increase.     

How does the extent of substitution of methane with chlorine influence the mechanism and kinetics of the reactions between chloromethanes and atomic chlorine

A theoretical investigation of the reaction mechanism and kinetics of the reaction between chloromethanes CH_4–xCl_x (x = 1–3) and chlorine atoms was performed. The height of the reaction barrier was found to decrease with the degree of substitution of chloromethanes with atomic chlorine. A direct dynamics method was employed to study the kinetic nature of these hydrogen-abstraction reactions. The sequence of calculated reaction rate coefficients is: k(CH₃Cl + Cl) < k(CH₂Cl₂ + Cl) < k(CHCl₃ + Cl).     

Synthesis,structural, spectral,thermal and comparative biological activity studies of [V<Subscript>2</Subscript>O<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>]

The hydrothermal reaction of a mixture of V₂O₅, VCl₃, 2,5-pyridinedicarboxylic acid and diluted H₂SO₄ for 68 h at 180°C gives a blue colored solution which yields prismatic blue crystals of IV ₂ ^IV O₂(SO₄)₂(H₂O)₆] (1) in 32% yield (based on V). Complex 1 was investigated by means of elemental analysis (C, H and S), TGA, FT-IR, manganometric titration, Single Crystal X-ray Diffraction Methods and also comparative antimicrobial activities. Crystal data for the compound: monoclinic space group P2₁/c and unit cell parameters are a = 7.3850(12) Å, b = 7.3990(7) Å, c = 12.229(2) Å, β = 108.976(12)° and Z = 2. Although structure of 1 as a natural mineral has been previously determined, this work covers new preparation method and full characterization of 1 along with comparison of antibacterial activity between 1 and the commercial vanadium(IV) oxide sulfate hydrate compounds, VOSO₄ · xH₂O (Riedel-de Haën and Alfa Aesar brand names). 1 was evaluated for the antimicrobial activity against gram-positive, gram-negative bacteria, yeasts and mould compared with the commercial VOSO₄ · xH₂O compounds. 1 showed weak activity against bacteria Bacillus cereus, Nocardia asteroides and yeast Candida albicans. A good antimicrobial activity was recorded against Cirtobacter freundii (15 mm). There are only a few reproducible well-defined vanadium(IV) starting materials to use for exploring the synthesis of new materials. VCl₄, VO(acac)₂, VOSO₄ · xH₂O and [V(IV)OSO₄(H₂O)₄] · SO₄ · [H₂N(C₂H₄)₂NH₂] are common starting materials for such applications. In addition to these compounds, 1 can be used as an oxovanadium precursor.     

Systems Li<Subscript>2</Subscript>O(Na<Subscript>2</Subscript>O)-CdO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>: Phase composition and phase diagrams

The subsolidus phase composition of the M₂O-CdO-V₂O₅ systems with M = Li or Na is studied. Double orthovanadates MCdVO₄ and MCd₄(VO₄)₃ form solid solutions of composition Li_{1 ? 2x/3}Cd _x/3CdVO₄ (0 ≤ x ≤ 1, orthorhombic space group Cmcm, modulation at x = 0.6) and Na_{3 ? 2x} Cd_{3 + x} (VO₄)₃ (0 ≤ x ≤ 0.10 and 0.30 ≤ x ≤ 1, orthorhombic space group Cmcm and Pn2₁ a or Pnma, respectively). In the range 0.10 < x < 0.30, the end-members of the solid solutions coexist. Isothermal sections of the systems are mapped.     

Alkali (alkaline-earth) metal,aluminum, and titanium complex orthophosphates: Synthesis and characterization

Phase formation in the A_{1 + x} Al _x Ti_{2 ? x} P₃O₁₂ (A = Li, Na, K, Rb, or Cs; 0 ≤ x ≤ 2.0) and B_{0.5(l + x)}Al _x Ti_{2 ? x} P₃O₁₂ (B = Mg, Ca, Sr, or Ba; 0 ≤ x ≤ 2.0) systems was studied using X-ray powder diffraction, electron probe microanalysis, and IR spectroscopy. The following double and triple orthophosphates were found to exist: A_{1 + x} Al _x Ti_{2 ? x} (PO₄)₃ with A = Li (0 ≤ x ≤ 0.3), Na (0 ≤ x ≤ 1.0), K (x = 0, 1.0, or 2.0), Rb (x = 0, 1.0, or 2.0), or Cs (0 ≤ x ≤ 1.0) and B_{0.5(l + x)}Al _x Ti_{2 ? x} (PO₄)₃ with B = Mg and Ba (x = 0), Ca and Sr (0 ≤ x ≤ 0.2). These orthophosphates crystallize in the structure types of kosnarite, langbeinite, cesium titanium arsenate, potassium aluminum phosphate, or rubidium aluminum phosphate. Their crystal parameters were calculated. For CsTi₂(PO₄)₃ (x = 0), Rietveld refinement was carried out: space group Ia \(\bar 3\) d, Z = 32, a = 19.909(5) Å, V = 7892(1) ų. This compound has a framework structure. The framework is built of TiO₆ octahedra and PO₄ tetrahedra; eight- and 12-coordinated Cs⁺ cations populate interstices.     

Synthesis and study of solid solutions between cobalt and nickel phosphates with varied degree of anion protonation

Continuous substitutional solid solutions between cobalt and nickel phosphates with varied degree of anion protonation were obtained: Co_1?x Ni _x HPO₄·1.5H₂O and (Co_1?x Ni _x )₃(PO₄)₂·8H₂O, where 0 ≤ x ≤ 1.00. The thermolysis of the solid solutions was studied by the example of Co_1?x Ni _x HPO₄·1.5H₂O. The phases synthesized were compared with the previously described continuous solid solution Co_1?x Ni _x (H₂PO₄)₂·2H₂O.     

Specific features of La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> solid state synthesis

Investigations of solid state preparation of La_1?xMnO₃ compounds (_x = 0, 0.1, 0.14, 0.17, 0.23) has revealed a number of intermediate structural states connected with progressive ordering of crystal structures. Freshly prepared non-stoichiometric compounds (x ≠ 0) are characterized by Mn⁴⁺ inclusion (0.09 ≤ y(Mn⁴⁺) 0.24) and rhombohedral space group \(R\bar 3c\).     

Glass-forming ability and thermal stability of Se<Subscript>100−x</Subscript>(Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript>)<Subscript>x</Subscript> glassy alloys

Glassy Se_100?x(Ge₂Sb₂Te₅)_x (x?=?5, 10, 15 and 20) bulk alloys were prepared by melt-quenched technique and studied by using differential scanning calorimetry at different heating rates under non-isothermal condition. The detailed thermal analysis shows that the glass transition temperature (T_g) depends on heating rates and x content. In particular, it is found that the glass-forming ability, thermal stability (T_c???T_g) and crystallization activation energy (E_c) increase with increased x content in amorphous Se, whereas glass transition activation energy (E_g) and fragility index (F) decrease with increased x contents. Variation in these parameters can be explained on the basis of network-forming ability of Se and bonding arrangement among the constituent atoms of alloys.     

X-ray study of rhodium(III) sulfates

Compounds with compositions [Rh(H₂O)₆]₂(SO₄)₃·4H₂O (I), (H₃O)[Rh(H₂O)₆](SO₄)₂ (II), [Rh(H₂O)₅OH](SO₄)·0.5H₂O (III), and [Rh(H₂O)₆]₂(SO₄)·(H₂SO₄) _x ·5H₂O (IV) have been studied. The crystal structures of II, III, and IV were determined. All compounds crystallized in the monoclinic crystal system. Crystal data for II: a = 7.279(2) Å, b = 10.512(7) Å, c = 15.806(3) Å, β = 96.71(3)°, space group P2₁/n, Z = 2, d _calc = 2.334 g/cm³; III: a = 20.433(4) Å, b = 7.820(2) c = 11.215(2) Å, β = 114.14(1)°, space group C2/c, Z = 8, d _calc = 2.559 g/cm³; IV: a = 6.2250(4 Å), b = 27.0270(12) Å, c = 7.2674(5) Å, β = 97.04(3)°, space group P2₁/c, Z = 4, d _calc = 2.143 g/cm³. The compounds were studied by IR spectroscopy and powder X-ray diffraction. All of the isolated crystalline phases are sparingly soluble in ethanol and well soluble in water.     

Low-temperature heat capacity and high-temperature thermal behavior of sodium lutetium molybdate phosphate Na<Subscript>2</Subscript>Lu(MoO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)

The low-temperature heat capacity of Na₂Lu (MoO₄)(PO₄) was measured by adiabatic calorimetry in the range of 7.47–345.74 K. The experimental data were used to calculate the thermodynamic functions of Na₂Lu (MoO₄)(PO₄). At 298.15 K, the following values were obtained: C _p ⁰ (298.15 K) = 237.7 ± 0.1 J/(K mol), S ⁰(298.15 K) = 278.1 ± 0.8 J/(K mol), H ⁰(298.15 K) ? H ⁰ (0 K) = 42330 ± 20 J/mol, and Φ⁰(298.15 K) = 136.1 ± 0. 3 J/(K mol). A heat capacity anomaly was found in the range of 10-67 K with a maximum at T _tr = 39.18 K. The entropy and enthalpy of transition are ΔS = 12.39 ± 0.75 J/(K mol) and ΔH = 403 ± 16 J/mol. The thermal investigation of sodium lutetium molybdate phosphate in the high-temperature range (623–1223 K) was performed using differential scanning calorimetry. It was found that during melting in the range of 1030–1200 K, Na₂Lu(MoO₄)(PO₄) degrades to simpler compounds; the degradation scenario is verified by X-ray powder diffraction.