Electrochemical synthesis of ammonia using a cell with a Nafion membrane and SmFe0.7Cu0.3?xNixO3 (x = 0?0.3) cathode at atmospheric pressure and lower temperature

Samaria-doped ceria Ce_0.8Sm_0.2O_2−δ (SDC) and SmFe_0.7Cu_0.3−x Ni _x O₃ have been synthesized by the sol-gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The electrochemical synthesis of ammonia was investigated at atmospheric pressure and low temperature, using the SFCN materials as the cathode, a Nafion membrane as the electrolyte, nickel-doped SDC (Ni-SDC) as the anode and silver-platinum paste as the current collector. Ammonia was synthesized from 25 to 100°C when the SFCN materials were used as cathode, with SmFe_0.7Cu_0.1Ni_0.2O₃ giving the highest rates of ammonia formation. The maximum rate of evolution of ammonia was 1.13 × 10⁻⁸ mol·cm⁻²·s⁻¹ at 80°C, and the current efficiency reached as high as 90.4%. Supported by the National Natural Science Foundation of China (Grant No. 20863007)     

Novel BaCo0.7Fe0.3−yNbyO3−δ (y = 0–0.12) as a cathode for intermediate temperature solid oxide fuel cell

The BaCo_0.7Fe_0.3?yNb_yO_3?δ oxides (BCFNy, y = 0.00–0.12) were synthesized by the conventional solid state reaction process and investigated as a novel cathode for intermediate temperature solid oxide fuel cells(IT-SOFCs). Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y ? 0.04. The unit cell volumes increased with y, reached a maximum at y = 0.10, and then decreased. The niobium doping concentration also had a significant effect on the electrochemical performance of BCFNy materials. Among the various BCFNy oxides tested, BCFN0.10 possessed the smallest interfacial polarization resistance (R_p). The R_p was as low as 0.9406, 0.1300, 0.0211, and 0.0082 Ω cm² at 500, 600, 700, and 800 °C, respectively. With a 220 μm-thick Sm_0.2Ce_0.1O_1.9 (SDC) as electrolyte and BCFN0.10 as the cathode, a fuel cell provides maximum power densities of 202, 350, 569, 820, and 1006 mW cm^?2 at 600, 650, 700, 750, and 800 °C, respectively. The encouraging results suggested that BCFN0.10 was a very promising cathode material for IT-SOFCs.     

Chemical pressure and rare-earth orbital contributions in mixed rare-earth silicides La(5-x)Y(x)Si4 (0 ≤ x ≤ 5)

A crystallographic study and theoretical analysis of the structural and La/Y site preferences in the La(5-x)Y(x)Si(4) (0 ≤ x ≤ 5) series prepared by high-temperature methods is presented. At room temperature, La-rich La(5-x)Y(x)Si(4) phases with x ≤ 3.0 exhibit the tetragonal Zr(5)Si(4)-type structure (space group P4(1)2(1)2, Z = 4, Pearson symbol tP36), which contains only Si-Si dimers. On the other hand, Y-rich phases with x = 4.0 and 4.5 adopt the orthorhombic Gd(5)Si(4)-type structure (space group Pnma, Z = 4, Pearson symbol oP36), also with Si-Si dimers, whereas Y(5)Si(4) forms the monoclinic Gd(5)Si(2)Ge(2) structure (space group P2(1)/c, Z = 4, Pearson symbol mP36), which exhibits 50% "broken" Si-Si dimers. Local and long-range structural relationships among the tetragonal, orthorhombic, and monoclinic structures are discussed. Refinements from single crystal X-ray diffraction studies of the three independent sites for La or Y atoms in the asymmetric unit reveal partial mixing of these elements, with clearly different preferences for these two elements. First-principles electronic structure calculations, used to investigate the La/Y site preferences and structural trends in the La(5-x)Y(x)Si(4) series, indicate that long- and short-range structural features are controlled largely by atomic sizes. La 5d and Y 4d orbitals, however, generate distinct, yet subtle effects on the electronic density of states curves, and influence characteristics of Si-Si bonding in these phases.     

High pressure synthesis and structure of a novel clathrate-type compound: Te7+xSi20−x (x∼2.5)

A novel clathrate-type compound, Te_7+xSi_20+x (x∼2.5), has been synthesized from the elements under high pressure and high temperature conditions. Its structure has been solved by Rietveld analysis of the XRD powder patterns combined with the results of an electron diffraction study. This structure is closely related to that of a type I clathrate, but with a different unit-cell parameter (a∼2×a₀) and space group (Fd-3c instead of Pm-3n). Its main feature is that it corresponds to a double clathration of a Te atom enclosed in a partially Te substituted (12.5%) Si₂₀ pentagonal dodecahedra, which is itself enclosed in a large Te₂₄ polyhedron, in form of a truncated octahedron. This outer Te network proved to be similar to the characteristic H₂O host lattice of a type VII clathrate (HEF₆·(H₂O)₅·HF (E=P, As, Te)), the distribution of the Si/Al atoms in minerals of the sodalite group ((Na,Ca)₈(Al₆Si₆O₂₄)(Cl,S,SO₄)₂) and to the arrangement of the Ba atoms in the structure of the superconducting compound, Ba₆C₆₀. This new clathrate structure of silicon is the first one which exhibits Si₂₀ pentagonal dodecahedra which are only linked by inter-cluster bonds, a result which opens new prospects in the domain of the chemistry of macro-ions such as Si₂₀¹²⁺ or Si₂₈⁴⁺.     

Liquid phase equilibria for mixtures of (an aliphatic hydrocarbon + toluene + γ-butyrolactone) at 298.2 K and atmospheric pressure

Liquid–liquid equilibrium (LLE) data for three ternary systems consisting of {n-heptane or n-hexane or cyclohexane (1) + toluene (2) + γ-butyrolactone (3)} were measured at 298.2 K and atmospheric pressure. The reliability of the experimental tie-line data was verified by using the Othmer–Tobias correlation. Distribution coefficients, separation factors and selectivity were evaluated for the immiscibility region. The experimental tie-line data were correlated by the UNIQUAC equation and also predicted with the UNIFAC model. The calculated results were compared with the experimental data. Better agreement with the experimental data was obtained by the UNIQUAC equation. The UNIFAC model does not provide reasonable correlations.     

Introducing a magnetic guest to a tetrel-free clathrate: synthesis, structure, and properties of Eu(x)Ba(8-x)Cu16P30 (0 ≤ x ≤ 1.5)

The europium-containing clathrate-I Eu(x)Ba(8-x)Cu(16)P(30) was synthesized from the elements. Powder X-ray diffraction in combination with energy dispersive X-ray absorption spectroscopy (EDXS) and metallographic studies showed the homogeneity range with x ≤ 1.5. Determination of the crystal structure confirmed the presence of an orthorhombic superstructure of clathrate-I and revealed that Eu atoms exclusively resided in small pentagonal-dodecahedral cages. Magnetic measurements together with X-ray absorption spectroscopy are consistent with a 4f(7) (Eu(2+)) ground state for Eu(x)Ba(8-x)Cu(16)P(30). Below 3 K the Eu moments order antiferromagnetically. Resistivity measurements revealed metallic behavior of the investigated clathrate, in line with the composition deviating from the Zintl counting scheme. Local vibrations of the guest atoms inside the cages are analyzed with the help of specific heat investigations.     

A room temperature solid-state rechargeable sodium ion cell based on a ceramic Na-β″-Al2O3 electrolyte and NaTi2(PO4)3 cathode

In this work, a room temperature solid-state rechargeable sodium ion cell, consisting of a ceramic Na-β″-Al₂O₃ thin film as the electrolyte, a NaTi₂(PO₄)₃ gel composite as the cathode and sodium metal as the anode, was developed for the first time. A dense Na-β″-Al₂O₃ thin film with a thickness of approximately 100 μm was obtained by non-toxic and hazard-free ceramic fabrication processes, including tape-casting and subsequent sintering. The solid-state sodium ion cell had a working window of 1.5–2.5 V upon charge-discharge processes and exhibited an extremely stable voltage plateau of approximately 2.1 V. A reversible capacity, based on the NaTi₂(PO₄)₃ cathode, of 133 mAh g^− 1 was observed during the first cycle, which remained approximately 100 mAh g^− 1 after 50 cycles.     

Phase pure (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 nanocrystalline particles synthesized by sol–gel technique at low temperature and their application

Phase pure (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ (BSZN) perovskite ceramic nanocrystalline particles were synthesized at low temperature with high reaction yield and high synthetic reproducibility using the sol–gel technique. The results showed that high-purity perovskite BSZN phase with high crystalline quality was obtained at 800 °C, that is, the volatilization of ZnO was successfully overcome. The nanocrystalline particles were about 20–30 nm in diameter with regular and uniform spherical shapes, high dispersive properties, and less aggregation. The pellets made by these nanoparticles had excellent dielectric properties: dielectric constant $ \varepsilon_{\text{r}} $ 40.5, temperature coefficient of resonant frequency $ \tau_{\text{f}} $  0.5 × 10^?6/ °C, and quality factor Q × f: 75,000 at 3.89 GHz, and a high relative density of 98.1 %.     

A simple synthesis and room temperature magnetic properties of new binary Mn0.5Fe0.5(H2PO4)2·xH2O obtained from a rapid co-precipitation at ambient temperature

A new binary Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O powder was synthesized by simple and cost-effective method using phosphoric acid, manganese and iron metals as starting chemicals. The synthesized solid shows the complex thermal transformations and the final decomposition product is a new binary manganese iron cyclo-tetraphosphate, MnFeP₄O₁₂. The X-ray diffraction and FTIR results indicate that the synthesized new binary Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and the decomposition MnFeP₄O₁₂ powders are a pure monoclinic phase with space group P2₁/n (Z = 2) and C2/c (Z = 4), respectively. The particle morphologies of Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and MnFeP₄O₁₂ powders appear as the rod-like tetragonal shape and show a high agglomeration of small particles, which are similar to the case of Mn(H₂PO₄)₂·2H₂O and Fe₂P₄O₁₂, respectively. Room temperature magnetization results show a ferromagnetic behavior of the Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and MnFeP₄O₁₂ powders, having the hysteresis loops in the range of ?10,000 Oe < H < +10,000 Oe with the specific magnetization values of 25.63 and 13.14 emu/g at 10 kOe, respectively. The lower magnetizations of Mn_0.5Fe_0.5(H₂PO₄)₂·xH₂O and MnFeP₄O₁₂ than those of Fe(H₂PO₄)₂·2H₂O and Fe₂P₄O₁₂ powders indicate the presence of Mn ions in substitution position of Fe ions.     

Complete titanium substitution by boron in a tetragonal prism: exploring the complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) by experiment and theory

Polycrystalline samples and single crystals of four members of the new complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti(3)Co(5)B(2) structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti(3)Ru(2.9)Ir(2.1)B(2)). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti(2)Ru(2.8)Ir(2.2)B(3)). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir-B and Ru/Ir-Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides.     

Magnetic and luminescent properties of copper-deficient Cu1–x(In0.7Ga0.3)Se2 (0 < x ⩽ 0.32) solid solutions with chalcopyrite structure

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Bi7−xAs1+xMo3O21 (0⩽x⩽1) a new pillar structure type: synthesis,crystal structure and conductivity

An original structure of chemical formula Bi₁₃As₃Mo₆O₄₂ has been obtained in the system Bi₂O₃:MoO₃:As₂O₃ by chemical transport reaction in presence of As₂O₃. It crystallizes in the monoclinic system, space group P2₁/n with a=12.7770(11) Å, b=5.5890(4) Å, c=27.971(2) Å and β=101.009(7)°. The structure exhibits infinite [Bi₁₃As₃Mo₆O₄₂]_n complex pillars with a quite different organization compared with original [Bi₁₂O₁₄]_n⁸ⁿ⁺ columns surrounded by (MoO₄) tetrahedra in the Bi_2/3[Bi₁₂O₁₄](MoO₄)₅ prototype structure. Nevertheless, the heavy atoms design almost perfect fluorite subnetwork—a common structural feature of these pillar structures. The conditions of synthesis via solid-state chemistry using basic oxides Bi₂O₃, As₂O₃ and MoO₃ have been established and the phase identified by X-ray powder pattern. The indexing fits single crystal data as well as the values of volumic mass, ρ_exp=7.04(4) g cm⁻³ for ρ_X=7.096 g cm⁻³ for Z=4. This Bi₁₃As₃Mo₆O₄₂ phase shows also an interesting anionic conductivity around σ=7.98×10⁻⁴ S cm⁻¹ at 980 K and is compared with related phases.     

Structural and dynamical studies of δ-Bi2O3 oxide ion conductors: III. Phase relationships in the system (Bi2O3)1−x(M2O3)x as a function of pressure and temperature (M = Y,Er, or Yb)

We report the results of a structural investigation of the nonstoichiometric solid solutions (Bi₂O₃)_1−x(M₂O₃)_x (M = Y, Er, or Yb) treated at temperatures of between 298 and 1023 K and at pressures of up to 4 GPa. For x = 0.25 and M = Er or Y, 4 GPa pressure at 873 K causes the fluorite-related phase stable under ambient conditions to transform to a monoclinic phase which on subsequent annealing transforms to a rhombohedral phase isostructural with that adopted by the solid solution (Bi₂O₃)_1−x(Sm₂O₃)_x under ambient conditions. For x = 0.4 and M = Er or Y, application of 4 GPa at 1073 K causes the fluorite phase to undergo a distortion to another rhombohedral structure with a smaller unit cell. No transitions were found in the Yb³⁺-doped system.     

Synthesis and characterization of Ni0.7−xMnxZn0.3Fe2(C4H2O4)3·6N2H4 (x = 0.1–0.6): A precursor for the synthesis of nickel–manganese–zinc ferrites

Journal of Thermal Analysis and Calorimetry - Spinel ferrites are the technologically important materials whose application ranges from the environmental, bio-medical to the smart devices. The...     

Measurements of the(p,ρ,T) relation of methane and carbon dioxide in the temperature range 240 K to 520 K at pressures up to 30 MPa using a new accurate single-sinker densimeter

Comprehensive (p, ρ, T) measurements on pure methane (159 values) and pure carbon dioxide (118 values) have been carried out in the temperature range 240 K to 520 K at pressures up to 30 MPa. The measurements were performed by means of a single-sinker densimeter that is based on Archimedes’ buoyancy principle. The total relative uncertainty of the measurements in the density ρ was estimated to be⩽ |(1.5 to 2) · 10 ^− 4·ρ | for methane and⩽ |(2 to 3) · 10 ^− 4·ρ | for carbon dioxide. The measurements are compared with previous results of other experimentalists and with values calculated from current equations of state. Moreover, previously unpublished results of (p, ρ, T) measurements on carbon dioxide (29 values) and methane (53 values) are listed in the appendix.     

First-principles calculations of the structural,elastic and electronic properties of MNxC1−x (M = Ti,Zr, Hf; 0 ≤ x ≤ 1) carbonitrides at ambient and elevated hydrostatic pressure

The structural, electronic, and elastic properties of three mixed transition metal carbonitrides TiN_xC_1−x, ZrN_xC_1−x, and HfN_xC_1−x (0 ≤ x ≤ 1) with the rock-salt structure were calculated at ambient and elevated up to 50 GPa hydrostatic pressures in the framework of the density functional theory methods. The lattice constants, densities, and bulk moduli of the considered compounds were shown to behave as linear functions of the nitrogen concentration x. The obtained linear dependencies of all these parameters allow for getting their estimates at any value of x in the range from 0 to 1. Gradual enhancement of the ionicity of the chemical bonds with gradual replacement of carbon by nitrogen was demonstrated by calculating the bond orders and electron density difference distributions.     

Near critical measurements of HmEandVmE for { xCO2 + (1 − x)SF6} and measurements made over the pressure range 2.5 to 10.0 MPa at the temperature T = 301.95 K

A flow mixing calorimeter, followed by a vibrating tube densimeter, has been used to measure excess molar enthalpies H_m^Eand excess molar volumesV_m^E of {xCO₂ +  (1  − x)SF₆}. Measurements over a range of mole fraction x have been made at the temperatures T =  302.15 K and T =  305.65 K at the pressures (3.76, 5.20, 6.20, and 7.38) MPa. The lowest pressure 3.76 MPa is close to thecritical pressure of SF₆ and the highest pressure 7.38 MPa is close to the critical pressure of CO ₂. Measurements atx =  0.5 have been made over the pressure range (2.5 to 10.0) MPa at the temperature 301.95 K. Some of the measurements are very close to the critical locus of the mixture. The measurements are compared with the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on {xCO₂ +  (1  − x)C₂H₆} and{xCO₂ +  (1  − x)C₂H₄} . The equation was used to calculate residual enthalpies and residual volumes for the pure components and for the mixture, and inspection of the way these combine to give excess enthalpies and volumes assisted the interpretation of the pressure scan measurements.