Preparation and electrical properties of new oxide ion conductors Ce6−xDyxMoO15−δ (0.0 ≤ x ≤ 1.8)

Ce_6−xDy_xMoO_15−δ (0.0 ≤ x ≤ 1.8) were synthesized by modified sol–gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 °C and 800 °C indicated a sharp increase in conductivity for the system containing small amount of Dy₂O₃. The Ce_5.6Dy_0.4MoO_15−δ detected to be the best conducting phase with the highest conductivity (σ_t = 8.93 × 10⁻³ S cm⁻¹) is higher than that of Ce_5.6Sm_0.4MoO_15−δ (σ_t = 2.93 × 10⁻³ S cm⁻¹) at 800 °C, and the corresponding activation energy of Ce_5.6Dy_0.4MoO_15−δ (0.994 eV) is lower than that of Ce_5.6Sm_0.4MoO_15−δ (1.002 eV).     

Structures, vibrational frequencies, and electron affinities of SF5On/SF5On (n = 1–3)

The molecular structures, vibrational frequencies, and electron affinities of the SF₅O_n/SF₅O_n⁻ (n = 1–3) species have been examined with four hybrid density functional theory (DFT) methods. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. The SF₅O_n (n = 1–3) species should be potential greenhouse gases. The anion SF₅O₂⁻ with C_s symmetry has a ³A″ electronic state, and the neutral SF₅O₃ with ²A″ electronic state has C_s symmetry. The anions SF₅O₂⁻ and SF₅O₃⁻ should be regarded as SF₅⁻·O₂ and SF₅O⁻·O₂ complexes, respectively. Three different types of the neutral–anion energy separation presented in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The EA_ad values predicted by the B3PW91 method are 5.22 (SF₅O), 4.38 (SF₅O₂), and 3.61 eV (SF₅O₃). Compared with the experimental vibrational frequencies, the BHLYP method overestimates the frequencies, and the other three methods underestimate the frequencies. The bond dissociation energies D_e (SF₅O_n → SF₅O_n−m + O_m) for the neutrals SF₅O_n and D_e (SF₅O_n⁻ → SF₅O_n−m⁻ + O_m and SF₅O_n⁻ → SF₅O_n−m + O_m⁻) for the anions SF₅O_n⁻ are reported.     

Structure–composition sensitivity in “Metallic” Zintl phases: A study of Eu(Ga1−xTtx)2 (Tt=Si, Ge, 0≤x≤1)

Two isoelectronic series, Eu(Ga_1−xTt_x)₂ (Tt=Si, Ge, 0≤x≤1), have been synthesized and characterized by powder and single-crystal X-ray diffraction, physical property measurements, and electronic structure calculations. In Eu(Ga_1−xSi_x)₂, crystal structures vary from the KHg₂-type to the AlB₂-type, and, finally, the ThSi₂-type structure as x increases. The hexagonal AlB₂-type structure is identified for compositions 0.18(2)≤x<0.70(2) with Ga and Si atoms statistically distributed in the polyanionic 6³ nets. As smaller Si atoms replace Ga atoms while the number of valence electrons increases, the lattice parameters, unit cell volumes, and Ga–Si distances in this phase region decrease significantly. Although aspects of X-ray diffraction results suggest puckering of the 6³ nets for the Si-richest example of the AlB₂-type Eu(Ga_1−xSi_x)₂, the complete experimental evidence remains inconclusive. On the other hand, in Eu(Ga_1−xGe_x)₂, six different structural types were observed as x varies. In addition to EuGa₂ (KHg₂-type; space group Imma) and EuGe₂ (own structure type, space group P3¯m1), the ternary phases studied show four different structures: the AlB₂-type for Ga-rich compositions; the YPtAs-type structure for EuGaGe; and two new structures, which are intergrowths of the YPtAs-type EuGaGe and EuGe₂, for Ge-rich compositions. These two Ge-rich phases include: (1) Eu(Ga_0.45(2)Ge_0.55(2))₂ containing two YPtAs-type motifs of EuGaGe plus one EuGe₂ motif; and (2) Eu(Ga_0.40(2)Ge_0.60(2))₂ containing one YPtAs-type motif alternating with a split site at and z=0.4798(2) with ca. 50% site occupancy by Ga and Ge along the c-axis. Magnetic susceptibilities of three Eu(Ga_1−xGe_x)₂ compounds display Curie–Weiss behavior above ca. 100 K, and show effective magnetic moments indicative of divalent Eu with a 4f⁷ electronic configuration, consistent with. X-ray absorption spectra (XAS). Density of states (DOS) and crystal orbital Hamilton population (COHP) analyses, based on first principles electronic structure calculations, rationalize the observed homogeneity ranges of the AlB₂-type phases in both systems and the structural variations as a function of Tt content.     

Electronic spectra of the linear magnesium-containing carbon chains MgC2nH (n = 1–5): A CASPT2 study

Complete active space self-consistent-field (CASSCF) approach has been used for the geometry optimization of the X²Σ⁺ and A²Π electronic states for the linear magnesium-containing carbon chains MgC_2nH (n = 1–5). Multireference second-order perturbation theory (CASPT2) has been used to calculate the vertical excitation energies from the ground to selected seven excited states, as well as the potential energy curves of two ²Σ⁺ and two ²Π electronic states. The studies indicate that the vertical excitation energies of the A²Π ← X²Σ⁺ transition for MgC_2nH (n = 1–5) are 2.837, 2.793, 2.767, 2.714, and 2.669 eV, respectively, showing remarkable linear size dependence. Compared with the previous TD-DFT and RCCSD(T) results, our estimates for MgC_2nH (n = 1–3) are in the best agreement with the available observed data of 2.83, 2.78, and 2.74 eV, respectively. In addition, the dissociation energies in MgC_2nH (n = 1–5) are also been evaluated.     

Analysis of thermo-magnetic fluctuations above the glass-transition temperature in Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1O8+δ (0.000 ≤ x ≤ 0.180) system

The resistivity of Bi_1.6Pb_0.5Sr_2−xEu_xCa_1.1Cu_2.1O_8+δ (0.000 ≤ x ≤ 0.180) superconductor has been measured as a function of temperature and magnetic field. The resistivity shows a glassy behavior even at higher temperatures and magnetic fields for the Eu-doped samples as compared with the Eu free sample. The values of glass-transition temperature [T_g], magnetic field dependent activation energy [U₀(B)] and the temperature and magnetic field dependent activation energy [U₀(B,T)] are found to be maximum for optimal doping levels (x = 0.135) which shows that the flux lines are effectively pinned in this sample. Also for temperatures below the superconducting transition temperature (T_C), a scaling of measured resistivity curves in magnetic field (B = 0.4 and 0.8 T) is obtained and this scaling is quite useful for better understanding of the behavior of the flux vortices in high temperature superconductors.     

Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1−5)

The density functional theory (DFT) and the complete active space self‐consistent‐field (CASSCF) method have been used for full geometry optimization of carbon chains C_2nH⁺ (n = 1–5) in their ground states and selected excited states, respectively. Calculations show that C_2nH⁺ (n = 1–5) have stable linear structures with the ground state of X³Π for C₂H⁺ or X³Σ^? for other species. The excited‐state properties of C_2nH⁺ have been investigated by the multiconfigurational second‐order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low‐lying states in C_2nH⁺ (n = 1–5). Present results indicate that the predicted vertical excitation and emission energies of C_2nH⁺ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Structure and Magnetism of Pr1−xSrxFeO3−δ

Crystal structure, redox, and magnetic properties for the Pr_1−xSr_xFeO_3−δ solid-solution phase have been studied. Oxidized samples (prepared in air at 900°C) crystallize in the GdFeO₃-type structure for 0≤x≤0.80, and probably in the Sr₈Fe₈O₂₃-type (unpublished) structure for x=0.90. Reduced samples (containing virtually only Fe³⁺) crystallize as the perovskite aristotype for x=0.50 and 0.67 with randomly distributed vacancies. The Fe⁴⁺ content increases linearly in the oxidized samples up to x≈0.70, whereupon it stabilizes at around 55%. Antiferromagnetic ordering of the G type is observed for oxidized samples (0≤x≤0.90) which show decreasing Néel temperature and ordered magnetic moment with increasing x, while the Néel temperature is nearly constant at 700 K for reduced samples. Electronic transitions for iron from an average-valence state via charge-separated to disproportionated states are proposed from anomalies in magnetic susceptibility curves in the temperature ranges 500–600 K and 150–185 K.     

The defect solid solution Na7/8(Fe7/8+xTi9/8−2xSbx)O4 (0 ≤ x ≤ 1/3): Evidence of Na mobility in the tunnels of a quadruple rutile-chain structure

A new defect solid solution, the series Na_7/8(Fe^III_7/8+xTi^IV_9/8−2xSb^V_x)O₄, was synthesized. Its homogeneity range is rather wide: 0 <- x ≤ 0.33. The incorporation of Sb^V gives rise to a progressive increase of the parameters of the orthorhombic unit cell. X-ray powder structure calculations point to a partial occupancy of the large double tunnels in a quadruple rutile-chain structure. A significant ordering of cations over the octahedral framework is observed, owing to a Ti^IV---Sb^V segregation. Electrical measurements emphasize a cationic conductivity, mainly related to a 1D motion of Na^I cations. A transition from a low activation energy process—E_A ≤ 0.20 eV—to a high activation energy one—E_A ≈ 0.75 eV—systematically occurs at T ≈ 440°C, independent of the Sb^V concentration. A possible skew motion from a half tunnel to another one is proposed as a tentative explanation of the high-temperature conductivity mechanism.     

Pillaring of Layered Perovskites, K1−xLaxCa2−xNb3O10, with Nanosized Fe2O3 Particles

Nanosized Fe₂O₃ clusters are pillared in the interlayer spaces of layered perovskites, H_1−xLa_xCa_2−xNb₃O₁₀ (0≤x≤0.75) by a guest-exchange reaction using the trinuclear acetato-hydroxo iron cation, [Fe₃(OCOCH₃)₇ OH·2H₂O]⁺. The interlayer spaces of niobate layers are pre-expanded with n-butylammonium cations (n-C₄H₉NH⁺₃), which are subsequently replaced by bulky iron pillaring species to form Fe(III) complex intercalated layer niobates. Upon heating at 380°C, the interlayered acetato-hydroxo iron complexes are converted into Fe₂O₃ nanoclusters with a thickness of ca. 3.5 Å irrespective of the interlayer charge density (x). The band-gap energy of the Fe₂O₃ pillars (E_g2.25 eV) is slightly larger than that of bulk Fe₂O₃ (E_g2.20 eV) but is smaller than that expected for such a small-sized semiconductor, which can be assigned to the pancake-shaped Fe₂O₃ pillars of 3.5 Å in height with comparatively large lateral dimension. X-ray absorption spectroscopic measurements at the Fe K-edge are carried out in order to obtain structural information on the Fe₂O₃ pillars stabilized between the niobate layers. XANES analysis reveals that the interlayer FeO₆ octahedra have coordination environments similar to that of bulk α-Fe₂O₃, but noncentrosymmetric distortion of interlayered FeO₆ is enhanced due to the asymmetric electric potential exerted by the negatively charged niobate layers. Scanning electron microscopic observation and nitrogen adsorption–desorption isotherm measurement suggest that the pillared derivatives are nanoporous materials with the highest BET specific surface area of ca. 116 m²/g.     

Theoretical study of electronic spectra of linear carbon clusters HC2nS (n = 1–5)

In this work we report the structures and stabilities of linear carbon clusters HC_2nS (n = 1–5) in their ground states using the B3LYP density functional. The rotational constants at the optimized geometries give excellent agreement with the experimental and previous theoretical values. The vertical excitation energies of the 2²Π ← X²Π transitions at the CASPT2 level are 3.16, 2.66, 2.05, 1.78, and 1.55 eV, respectively, in good agreement with the corresponding observed values of 3.01, 2.48, 2.10, 1.84, and 1.65 eV. Also, the exponential-decay curves for these vertical excitation energies obtained from experiments and theoretical calculations are illuminated.     

Determination of C4–C14 carboxylic acids by capillary zone electrophoresis: Application to the identification of diamide degradation products and partitioning studies

Capillary zone electrophoresis (CZE) was investigated for the determination of linear saturated carboxylic acid homologues ranging from C₄ to C₁₄. Separation conditions were optimised to overcome the problems of decreasing solubility and decreasing selectivity between successive homologues with increasing chain length. Separations were performed at 20°C, using a 20 kV separation voltage and a pH 8 electrolyte containing 30% methanol. A suitable chromophore (4-aminobenzoate) was added to ensure indirect UV detection of the analytes. Calibration curves and repeatability were established. Minimum detectable concentrations of 3·10⁻⁶ mol l⁻¹ were achieved. Resolution between successive homologues was better than 2. The electrophoretic mobility of each homologue (n=7–14) was assessed and a quasi-linear relationship between the mobility value and 1/n was observed. The quantitative analysis of a diamide degradation solution was performed and compared to potentiometric results. The CZE method was also applied to the determination of C₇–C₁₄ partitioning between an organic medium containing tributylphosphate in n-dodecane and different basic solutions. Their behaviour was established according to the chain length and the pH of the aqueous phase. For C₁₀–C₁₄ compounds, results were validated by comparison with gas chromatographic analysis of the organic phases.     

Mechanochemical Synthesis of LaOX (X=Cl, Br) and Their Solid State Solutions

A mixture of lanthanum oxide (La₂O₃), chloride (LaCl₃), and bromide (LaBr₃) was ground in air by a planetary ball mill to investigate synthesis of lanthanum oxychloride (LaOCl), oxybromide (LaOBr), and their solid solutions, LaOCl_1−xBr_x (0≤x≤1, Δx=0.25). The synthesizing reactions proceed with an increase in grinding time. Unit cell dimensions, a, c, and lattice volume of the solutions evolve linearly with an increase in x in the LaOCl_1−xBr_x series. Comparing unit cell dimensions of LaOX synthesized by mechanochemical reaction to those of LaOX synthesized by solid-state reaction at high temperature, there is no difference in the length of c, while a is shortened slightly. This may be attributed to the complex cation layer of (LaO)ⁿ⁺_n, with a close relationship to a of the cell dimensions, being affected by the intensive grinding.     

Evidence for charge exchange between N and N2(A Σu) in a low-temperature nitrogen plasma

The emission from the first negative system, N₂⁺(B ²Σ⁺_u)→N₂⁺(X ²Σ⁺_g)+hν, is studied in the flowing nitrogen afterglow of a DC arc plasma. Investigation of the spectrum shows overpopulation of the vibrational levels 6 and 7 of the excited molecular ion, N₂⁺(B ²Σ⁺_u). Selective excitation of these levels is explained by a charge exchange reaction between atomic ions in the ground state and metastable molecules in the N₂(A ³Σ⁺_u) state. The emitted intensity of the first negative system is shown to be linear with electron density n_e for n_e>2×10¹⁶ m⁻³, a higher-order dependence exists below this value. This is consistent with population of N₂⁺(B ²Σ⁺_u) by atomic ions, N⁺.     

Parity alternation of interstellar molecules cyanopolyynes HCnN (n = 1–17)

In this paper, we report the design of models for interstellar molecules HC_nN (n = 1–17) by means of the B3LYP density functional method. We performed geometry optimization and calculation on vibrational frequency. We find that the ground-state (G-S) isomers of HC_nN (n = 1–17) are with the N atom located at one end and the H atom at the other end of a C_n chain; they are all linear except for HC₂N which is bent. When n is odd, the C_n chain is polyacetylene-like whereas when n is even, the C_n chain displays a structure that is cumulenic-like in the middle of the C_n chain. It is found that the G-S isomers of odd-n HC_nN (n = 1–17) are more stable than those of even-n ones. The finding is in accord with the relative intensities of HC_nN recorded in laboratory investigations, and in consistent with the results of objects observed in interstellar media. We provide explanations for such a trend of even/odd alternation based on concepts of the highest vibrational frequency, bonding character, electronic configuration, incremental binding energy, nucleus-independent chemical shift, and dissociation channels.     

Electrochemical, spectroelectrochemical and theoretical studies on the reduction and deprotonation of the photovoltaic sensitizer [(H3-tctpy)Ru(NCS)3] (H3-tctpy=2,2′:6′,2′′-terpyridine-4,4′,4′′-tricarboxylic acid)

The electrochemical reduction of the black dye photosensitizer [(H₃-tctpy)Ru^II(NCS)₃]⁻ (H₃-tctpy=2,2′:6′,2′′-terpyridine-4,4′,4′′-tricarboxylic acid) used in photovoltaic cells has been found to be a complex process when studied in dimethylformamide. At low temperatures, fast scan rates and at a glassy carbon electrode, the chemically reversible ligand based one-electron reduction process [(H₃-tctpy)Ru(NCS)₃]⁻+e⁻[(H₃-tctpy√⁻)Ru(NCS)₃]²⁻ is detected. This process has a reversible half-wave potential (E^r_1/2) of −1585±20 mV versus Fc/Fc⁺ at 25°C. Under other conditions, a deprotonation reaction occurs upon reduction, which produces [(H_3−x-tctpy^x−)Ru(NCS)₃]^(1+x)− and hydrogen gas. Mechanistic pathways giving rise to the final products are discussed. The E^r_1/2-value for the ligand based reductions of the deprotonated complex is 0.70 V more negative than for [(H₃-tctpy)Ru(NCS)₃]⁻. Consequently, data obtained from molecular orbital calculations are consistent with the reaction [(H₃-tctpy)Ru(NCS)₃]⁻+e⁻→[(H₂-tctpy⁻)Ru(NCS)₃]²⁻+1/2H₂ yielding the monodeprotonated complex as the major product obtained after electrochemical reduction of [(H₃-tctpy)Ru(NCS)₃]⁻. The E^r_1/2-values for the metal based Ru^II/III process differ by 0.30 V when data obtained for the protonated and deprotonated forms of the black dye are compared. Electronic spectra obtained during the course of experiments in an optically transparent thin layer electrolysis configuration are consistent with the overall reaction scheme proposed on the basis of voltammetric measurements and molecular orbital calculations. Reduction studies on the free ligand, H₃-tcpy, are consistent with results obtained with [(H₃-tctpy)Ru(NCS)₃]⁻.     

Orthorhombic–orthorhombic phase transitions in Nd2NiO4+δ (0.067≤δ≤0.224)

Variation of the phases of Nd₂NiO_4+δ with the excess oxygen concentration δ has been examined at room temperature in the range 0.067≤δ≤0.224 using the X-ray powder diffraction technique. The phases observed at room temperature are orthorhombic-I (0.21<δ≤0.224), orthorhombic-IV (0.175<δ≤0.21), orthorhombic-II (0.15<δ≤0.175), orthorhombic-II+quasi-tetragonal-I (0.10<δ≤0.15), and quasi-tetragonal-I (0.067<δ≤0.10).     

Crystal chemistry, modulated structure, and electrical conductivity in the oxygen excess scheelite-based compounds La1−xThxNbO4+x/2 and LaNb1−xWxO4+x/2

For La_1−xTh_xNbO_4+x/2, three phases with broad homogeneity regions occur, for 0.075 ≤ x ≤ 0.37, 0.41 < x < 0.61, and 0.65 ≤ x ≤ 0.74. All are related to the scheelite structure type, with at least the first exhibiting an incommensurate structural modulation. An analogous structurally modulated phase was found for LaNb_1−xW_xO_4+x/2 for 0.11 ≤ x ≤ 0.22. Additional phases occur at La_0.2Th_0.8NbO_4.4 and LaNb_0.4W_0.6O_4.3. The electrical conductivity and the direction and wavelength of the structural modulation have been characterized for the La_1−xTh_xNbO_4+x/2 phase with 0.075 ≤ x ≤ 0.37.     

Synthesis, EPR spectrum and X-ray structure of tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κS,S′)platinate(III)

The new salt, tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κ²S,S′)platinate(III), [NBu₄][Pt(C₆H₄S₂)₂] (1), has been synthesized in ethanol/water, and fully characterized by single crystal X-ray structure determination. The central platinum in the complex ion [Pt(bdt)₂]⁻ is tetracoordinated by the S atoms of the bdt²⁻ ligands (bdt²⁻ is benzene-1,2-dithiolate) in a square-planar geometry. The well-resolved frozen solution EPR spectrum exhibits rhombic symmetry. The room temperature effective magnetic moment (μ_eff = 1.80 Bohr magneton) is in line with this spectrum and strongly supports the Pt(III) oxidation state in 1. This observation is in excellent agreement with previous results reported on closely related Ni(III), Pd(III) and Pt(III) species.     

Unusual stabilization of cationic “M(η-allyl) (M = Pt, Pd) units by a dianionic cis-{Pt(C6F5)2(CCSiMe3)2} fragment

Chloride abstraction from [{M(η³ --- C₃H₅)Cl}_n] (M = Pt, n = 4 or M = Pd, n = 2) by (NBu₄)₂[cis-Pt(C₆F₅)₂(CCSiMe₃)₂] (1) gives rise to novel homo- and hetero-dinuclear zwitterionic derivatives (NBu₄) [{cis-Pt(C₆F₅)₂(CCSiMe₃)₂}M(η³-C₃H₅)] (M = Pt 2; M = Pd 3) which are formed by a M(η³-allyl)⁺ unit attached to both alkynyl ligands of the {cis-Pt(C₆F₅)₂(CCSiMe₃)₂}²⁻ fragment. The structure of 3 has been established by X-ray diffraction.     

Transport through a slab membrane governed by a concentration-dependent diffusion coefficient: Part IV. D(C)/D0=1+(αC)−β(αC)

Using the specific functional form D(C)/D₀=1+(αC)−β(αC)² an investigation has been made of (isothermal) transport through a slab membrane under ‘simple’ boundary conditions and governed by a diffusion coefficient, D(C), which, with increasing concentration, at first increases, passes through a maximum value and finally decreases. The flux, integral diffusion coefficient and concentration profile characteristic of steady-state permeation have been evaluated; special attention has been paid to the positions of such profiles in relation to the corresponding linear distribution associated with a constant diffusion coefficient.The corresponding transient-state transport has been studied within a framework of the time-lag ‘early-time’ and ‘ ’ procedures. Expressions for the ‘adsorption’ and ‘desorption’ time-lags are given. The concentration-dependence of these time-lags, of the (four) integral diffusion coefficients derived from them and of the arithmetic-mean time-lag ratios have been considered in some detail. The ‘early-time’ and ‘ ’ finite-difference procedures have likewise been employed to derive four further integral diffusion coefficients, so enabling a comparison to be made of the nine integral coefficients pertaining to established experimental techniques.Particular interest attaches to the situation for which n≡β(αC₀)=1 (where C₀ is the ingoing or upstream concentration of diffusant) resulting in D(C₀) being symmetrical about C₀/2. Some consideration has been given, in general, to features of transient-state transport when governed by a symmetrical D(C).