Hydrogen dynamics in polyethersulfone: A quasielastic neutron scattering study in the high-momentum transfer region

In a previous quasielastic neutron scattering study [I. Quintana, A. Arbe, J. Colmenero, B. Frick, Macromolecules 38 (2005) 3999] we characterized the hydrogen dynamics in glassy polyethersulfone as due to ‘fast processes’ plus flips and oscillations of the phenylene rings. Here we have extended this investigation by using thermal neutrons, that allowed exploring also much higher values of the momentum transfer Q. In the dynamic window accessed, a characterization as best accurate as possible of the fast dynamics is imperative in order to describe the experimental results, especially at very local length scales. While for Q ≲ 2.2 Å⁻¹ (i.e., in the range previously studied) the proposed model perfectly describes the experimental data with the same parameters deduced from the earlier work, in the high Q-range (Q ≈ 3.5–4 Å⁻¹) deviations are found. These could be overcome by assuming some kind of ‘effective softening’ of the fast process and slight deviations from harmonic behavior in the Q-dependence of the associated Debye–Waller factor.     

High frequency dynamics of an orientationally disordered molecular crystal

The dynamic structure factor of the polycrystalline plastic crystal 1-cyanoadamantane has been measured in the THz frequency region by inelastic X-ray scattering as a function of the exchanged momentum Q in the range 1–10 nm⁻¹ and as a function of the temperature in the two solid disordered phases: plastic crystal and glassy crystal. We find that the dispersion of the acoustic excitations is crystal-like in the two phases and that the attenuation Γ(Q) shows a negligible T dependence similarly to structural glasses and a Q^α behavior with 1.15 < α < 1.50 at variance with structural glasses characterized by a Q² dependence.     

Network structure of multi-component sodium borosilicate glasses by neutron diffraction

Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 − x)SiO_2. · xB₂O₃ · 25Na₂O · 5BaO · 5ZrO₂, x = 5–15 mol%. The maximum momentum transfer of the experimental structure factor was 30 Å⁻¹, which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed. The characteristic features of Si–O and Si–Si distributions are similar for all glassy samples, suggesting that the Si–O network consisting of tetrahedral SiO₄ units is highly stable even in the multi-component glasses. The B–O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 Å and 1.60 Å, the latter equals the Si–O distance. Coordination number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O–O distribution suggests a network configuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO₃ units, and the silicon rich network is formed by a mixed continuous network of ^[4]Si–O–Si^[4] with several different ^[4]B–O–Si^[4] and ^[3]B–O–Si^[4] linkages.     

Microdynamics of a monoatomic liquid metal

Modified microscopic theory of the collective dynamics of a simple liquid has been used to explain the recently observed accurate detailed coherent dynamical structure factor S(k, ω) of liquid Na at 390 K as measured by high resolution inelastic X-ray scattering (IXS) in the wave-vector, κ, range 1.5 nm^?1 ? κ ? 14.6 nm^?1. The computed values of detailed spectral lineshape of S(k, ω), the dispersion relation and the velocity of sound are in reasonable agreement with the corresponding experimental results. Variation of longitudinal viscosity with κ has also been reported.     

Dilithium dialuminium trisilicate phase obtained using coal bottom ash

The Li₂Al₂Si₃O₁₀ glass-ceramics well crystallized and with a regular morphology was produced starting from a mixture of Li₂CO₃, TiO₂, Al₂O₃ and coal bottom ash, after reducing the magnetite phase content. Its measured thermal expansion coefficient in the temperatures range from 25 °C to 300 °C is α_(25–300) = −23.4 × 10⁻⁷ °C⁻¹. This value is ≈18% smaller than that for the commercial lithium glass-ceramics (−23.4 × 10⁻⁷ °C⁻¹ to 50 × 10⁻⁷ °C⁻¹).     

High frequency collective dynamics in liquid potassium

We investigated by inelastic X-ray scattering the dynamical properties of molten potassium in a wide range of momentum transfer, Q, from 1 nm⁻¹ up to the main peak of the structure factor Q ≈ 17 nm⁻¹. The observed increase of sound velocity in the low Q region (1 < Q < 3 nm⁻¹), has been described within a model characterized by two distinct relaxation processes for the collective dynamics. The obtained results are discussed and compared with those from previous neutron scattering experiments. In particular, we associate the speed-up of the sound velocity to the ‘instantaneous’ disorder of the liquid as opposed to the argument, supported by some neutron scattering studies, of a transition from a liquid to solid like response of the system.     

Effect of silver doping on the electrical properties of a-Sb2Se3

This paper reports the effect of Ag-doping on electrical properties of a-Sb₂Se₃ in the temperature range 230–340 K and frequency range 5–100 kHz. The variation of transport properties with thermal doping has been studied. Ag-doping produces two homogeneous phases in the sample, which are found to be voltage dependent in the temperature range studied and frequency dependent in lower frequency region (0.1–10 kHz). Activation energy E_g and C′ [= σ₀ exp (γ/k), where γ, is the temperature coefficient of the band gap] calculated from dc conductivity has been found to vary from (0.42 ± 0.01) eV to (0.26 ± 0.01) eV and (4.11 ± 0.01) × 10⁻⁵ to (2.90 ± 0.02) × 10⁻⁶ Ω⁻¹ cm⁻¹ respectively. Ag-doping can be used to make the sample useful in device applications.     

Na–Pb liquid alloy structure at low lead concentrations: Neutron-diffraction studies

Na–Pb liquid alloys with the lead concentration of 1.5 and 7.9 at.%, and pure sodium as a reference system are studied by neutron-diffraction at 700 K. A characteristic prepeak of static structure factor, S(Q), at Q ∼ 1.2 Å⁻¹, known from neutron-diffraction studies of the Na–Pb alloys with the lead concentration of 20 at.% and higher, is not observed for the alloys under consideration. The experimental S(Q) values are compared with the results of molecular-dynamics simulations.     

High frequency dynamics of liquid bismuth

The dynamic structure factor S(Q, ω) of liquid Bi was measured at 580 K in the Q range from 0.15 to 0.6 Å⁻¹ using inelastic neutron scattering. The obtained spectra clearly demonstrate the existence of well defined longitudinal propagating modes. A positive dispersion is found in the low Q region, where the mode velocity undergoes a transition between the hydrodynamic value and a high frequency value 20% larger. The damping of the excitations does not follow the hydrodynamic Q² trend and is stronger than in any metallic liquid investigated so far. The quasielastic lineshape contains a broad Q-independent Lorentzian contribution, other than a small sharp peak, which has yet been observed in liquid Hg and Ga.     

Influence of hydrogen on the thermomechanical properties of a-CNx:H and a-CNx films deposited by glow discharge and ion beam assisted deposition

The coefficient of thermal expansion (CTE), Young’s modulus, Poisson’s ratio, stress and hardness of a-CN_x and a-CN_x:H were investigated as a function of nitrogen concentration. Hydrogenated films were prepared by glow discharge, GD, and unhydrogenated films were prepared by ion beam assisted deposition, IBAD. Using nanohardness measurements and the thermally induced bending technique, it was possible to extract separately, Young’s modulus and Poisson’s ratio. A strong influence of hydrogen, in a-CN_x:H films, was observed on the CTE, which reaches about ∼9 × 10⁻⁶ C⁻¹, close to that of graphite (∼8 × 10⁻⁶ C⁻¹) for nitrogen concentration as low as 5 at.%. On the other hand, the CTE of unhydrogenated films increases with nitrogen concentration at a much lower rate, reaching 5.5 × 10⁻⁶ C⁻¹ for 33 at.% nitrogen.     

Neutron diffraction study of sodium borosilicate waste glasses containing uranium

The effect of uranium oxide on the structure of sodium borosilicate host glasses has been studied by neutron diffraction. The samples were prepared by quenching the melted mixtures of composition 70 wt% [(65 − x)SiO₂ · xB₂O₃ · 25Na₂O · 5BaO · 5ZrO₂] + 30 wt% UO₃ with x = 5, 10 and 15 mol%. It was found, that the U-loaded glasses posses good glass and hydrolytic stability. An enhanced probability for inter-mediate atomic correlations at around 4.8 Å has been established. The RMC simulation of the neutron diffraction data is consistent with a model where the uranium ions are incorporated into interstitial voids in the essentially unmodified network structure of the starting host glass. The U–O atomic pair correlation functions show a sharp peak at around 1.7 Å, and several farther distinct peaks are at 2.8, 3.6 and 4.1 Å. The uranium ions are coordinated by six oxygen atoms in the 1.6–3.4 Å interval.     

Properties and structure of (1 − x)Li2O–xNa2O–Al2O3–4SiO2 glass systems

(1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses were studied for the progressive percentage substitution of Na₂O for Li₂O at the constant mole of Al₂O₃ and SiO₂. The crystallization temperature at the exothermic peak increased from 898 to 939 °C when the Na₂O content increases from 0 to 0.6 mol. The coefficient of thermal expansion and density of these as-quenched glasses increase from 6.54 × 10⁻⁶ °C⁻¹ to 10.1 × 10⁻⁶ °C⁻¹ and 2.378 g cm⁻³ to 2.533 g cm⁻³ when the Na₂O content increases from 0 to 0.4 mol, respectively. The electrical resistivity has a maximum value at Na₂O · (Li₂O + Na₂O)⁻¹ = 0.4. The activation energy of crystallization decreases from 444 to 284 kJ mol⁻¹ when the Na₂O content increased from 0 to 0.4 mol. Moreover, the activation energy increases from 284 kJ mol⁻¹ to 446 kJ mol⁻¹ when the Na₂O content increased from 0.4 to 0.6 mol. The FT-IR spectra show that the symmetric stretching mode of the SiO₄ tetrahedra (1035–1054 cm⁻¹) and AlO₄ octahedra (713–763 cm⁻¹) exhibiting that the network structure is built by SiO₄ tetrahedra and AlO₄.     

The collective dynamics of the ‘non-simple’ liquid metal Sn

The dynamic structure factor S(Q, ω) of liquid Sn was measured at 320 °C and 1000 °C in a Q-range between 2 nm⁻¹ and 30 nm⁻¹ using inelastic X-ray scattering. The obtained spectra clearly demonstrate the existence of longitudinal propagating modes in this liquid metal. At 320 °C a positive dispersion is found in the low Q-region, where the mode velocity is about 12% larger than the bulk adiabatic speed of sound. At 1000° this so-called ‘positive dispersion’ reduces to about 6%. The quasielastic lineshape contains a Gaussian contribution near the Q-positions of the first maximum in S(Q), which has not yet been reported in simple liquid metals like, e.g. the liquid alkalis. With increasing temperature, the relative Gaussian contribution increases and can be observed along a wider Q-range. This anomaly is related to a partially covalent nature of liquid Sn in analogy to other liquid non-simple metals.     

Coefficients of stationary ArF laser pulse absorption in fused silica (type III)

Weak stationary bulk absorption coefficients α^stat(Φ, f) in fused silica are measured directly in dependence on the ArF laser fluence Φ and repetition rate f by the laser induced deflection technique (LID). The absorption is quantified using a modified Beer’s law. The investigated samples show non-linear increases α^stat(Φ, f = const.) for 3 ⩽ Φ ⩽ 25 mJ cm⁻² pulse⁻¹ and α^stat(Φ = const., f) for 50 ⩽ f ⩽ 400 Hz. The experimental data are fitted by a rate equation model consisting of an equilibrium between E′ center generation and annealing. Generation occurs photolytically from SiH and strained SiO bonds via 1- and 2-photon absorption, respectively. Annealing is due to the reaction with atomic hydrogen and other reaction channels, e.g. ODC generation.     

Strontium environment transition in tin silicate glasses by neutron and X-ray diffraction

The effect of Sr modifier atoms on the structure of stannosilicate glasses of composition (Sr0)_x(SnO)_0.5−x(SiO₂)_0.5, with 0 ⩽ x ⩽ 0.15, has been studied using Mössbauer spectroscopy and neutron and X-ray diffraction. The tin is mostly in the Sn²⁺ state. The Sr–O bond length undergoes a step decrease from (2.640 ± 0.005) Å to (2.585 ± 0.005) Å as x increases from 0.10 to 0.15, indicating a decrease in co-ordination number from 8 to 7. A Sn–Sn distance of 3.507 ± 0.005 Å is revealed by a first-order difference calculation from the x = 0 sample. This is too short to be consistent with significant edge sharing of [SnO₃] trigonal pyramids.     

Properties of sodium-based ternary phosphate glasses produced from readily available phosphate salts

Three series of phosphate glasses were produced by melting together sodium phosphate salt (NaH₂PO₄) and the phosphate salts of either calcium (CaHPO₄), magnesium (MgHPO₄ · 3H₂O) or iron (FePO₄ · 2H₂O) in a 5% gold/95% platinum crucible at 1200 °C. The glass compositions were confirmed by EDX and XRD analysis. Glass transition temperature (T_g), density and durability in water were determined for all the compositions. Maximum metal oxide contents before devitrification were between 55% and 59% for CaO + Na₂O and 59% and 62% for MgO + Na₂O. The normalized equivalent for Fe₂O₃ + Na₂O was between 55% and 61%. Density values for the glasses lay between 2.49 and 2.75 g cm⁻³. T_gs lay between 295 °C and 470 °C. Degradation rates in deionized water at 37 °C lay between 0.03 g cm⁻² h⁻¹ for Na phosphate glasses and 9 × 10⁻⁶ g cm⁻² h⁻¹ for Ca phosphate glasses, 3 × 10⁻⁶ g cm⁻² h⁻¹ for Mg phosphate glasses and <3 × 10⁻⁶ g cm⁻² h⁻¹ for Fe phosphate glasses. The effect of metal addition on properties goes as Fe > Mg > Ca for degradation rates and T_g and Fe > Mg ≈ Ca for density. The change in properties with metal addition was seen to be linear for Fe and Ca additions but not with Mg addition. This is in agreement with the anomalous behavior of magnesium phosphate glasses.     

Human 17β-hydroxysteroid dehydrogenase-ligand complexes: crystals of different space groups with various cations and combined seeding and co-crystallization

Human estrogenic 17β-hydroxysteroid dehydrogenase (17β-HSD1) is responsible for the synthesis of active estrogens that stimulate the proliferation of breast cancer cells. The enzyme has been crystallized using a Mg²⁺/PEG (3500)/β-octyl glucoside system [Zhu et al., J. Mol. Biol. 234 (1993) 242]. The space group of these crystals is C2. Here we report that cations can affect 17β-HSD1 crystallization significantly. In the presence of Mn²⁺ instead of Mg²⁺, crystals have been obtained in the same space group with similar unit cell dimensions. In the presence of Li⁺ and Na⁺ instead of Mg²⁺, the space group has been changed to P2₁2₁2₁. A whole data set for a crystal of 17ß-HSD1 complex with progesterone grown in the presence of Li⁺ has been collected to 1.95 Å resolution with a synchrotron source. The cell dimensions are a=41.91 Å, b=108.21 Å, c=117.00 Å. The structure has been preliminarily determined by molecular replacement, yielding important information on crystal packing in the presence of different cations. In order to further understand the structure–function relationship of 17β-HSD1, enzyme complexes with several ligands have been crystallized. As the steroids have very low aqueous solubility, we used a combined method of seeding and co-crystallization to obtain crystals of 17β-HSD1 complexed with various ligands. This method provides ideal conditions for growing complex crystals, with ligands such as 20α-hydroxysteroid progesterone, testosterone and 17β-methyl-estradiol-NADP⁺. Several complex structures have been determined with reliable electronic density of the bound ligands.     

Structure of amorphous NaCl–glucose system studied by X-ray diffraction and IR methods

X-ray diffraction and diffuse reflection IR spectroscopic measurements have been carried out on amorphous NaCl–glucose mixtures, a-(NaCl)_x(glucose)_1−x, with x = 0, 0.05, 0.1 and 0.15, in order to obtain structural information on the intermolecular hydrogen-bonded interaction between glucose molecules affected by the presence of NaCl. The difference distribution function Δg^inter(r) was derived from the Fourier transform of the difference intermolecular interference term Δi^inter(Q) between X-ray intermolecular interference terms observed from amorphous NaCl-glucose and pure glucose samples. A negative peak appears at r ≈ 2.5 Å in the Δg^inter(r) observed for the 10 mol% NaCl sample, while, the Δg^inter(r) for the 15 mol% NaCl sample does not show pronounced negative peak. On the other hand, the IR spectra for the O–H stretching region (2300 ⩽ ν ⩽ 3800 cm⁻¹) indicate that hydrogen bonds between glucose molecules are significantly collapsed in the samples containing 5–15 mol% NaCl. These results imply that the contribution from the Na⁺⋯Cl⁻ contact ion pair is dominated in the 15 mol% NaCl sample.     

The effect of fluoride on the Fe2+/Fe3+-redox equilibrium in glass melts in the system Na2O/NaF/CaO/Al2O3/SiO2

Liquids with the base compositions (16 − x/2)Na₂O · xNaF · 10CaO · 74SiO₂ (x = 0, 1, 3, and 4) and (10 − x/2) · Na₂O · xNaF · 10CaO · yAl₂O₃ · (80 − y)SiO₂ (x = 0, 1, 3, 5 and y = 5 and 15) doped with 0.25 mol% Fe₂O₃ were studied by means of square-wave voltammetry in the temperature range from 1000 to 1500 °C. With increasing temperature, the redox equilibria were shifted to the reduced state. Also while increasing the alumina concentration, the Fe²⁺/Fe³⁺-redox equilibrium is shifted to the reduced state. In the soda-lime–silica melt the addition of fluoride shifts the equilibrium to the oxidized state, while in the aluminosilicate melts with 15 mol% Al₂O₃, the equilibrium is shifted to the reduced state. In the aluminosilicate melts with 5 mol% Al₂O₃, the equilibrium was not affected by the fluoride concentration. This is explained by the structure of the respective glass compositions.     

Conductivity percolation transition of Agx(Ge0.25Se0.75)100−x glasses

The ionic conductivity of several chalcogenide glasses increases abruptly with mobile ion addition from values typical of insulating materials (10⁻¹⁶–10⁻¹⁴ Ω⁻¹ cm⁻¹) to values of fast ionic conductors (10⁻⁷–10⁻¹ Ω⁻¹ cm⁻¹). This change is produced in a limited concentration range pointing to a percolation process. In a previous work [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259] the transition from semiconductor to fast ionic conductor of Ag_x(Ge_0.25Se_0.75)_100−x glasses was detected at x¹ ≅ 10 at.% in the form of a steep change in the conductivity. Ag_x(Ge_0.25Se_0.75)_100−x glasses with x ⩽ 25 at.%, prepared by a melt quenching method, are investigated by impedance spectroscopy in the frequency range 5 Hz–2 MHz at different temperatures, T, from room temperature to 363 K and by DC measurements at room temperature. The conductivity of the glasses, σ, was obtained as a function of silver concentration and temperature. For x ⩾ 10 at.% our results are in agreement with those reported by Kawasaki et al. [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259]. The percolation transition was observed in the range 7 ⩽ x ⩽ 8. The temperature dependence of the ionic conductivity follows an Arrhenius type equation σ = (σ_o/T) · exp(−E_σ/kT). The activation energy of the ionic conductivity, E_σ, and the pre-exponential term, σ_o, are calculated. The results are discussed in connection with other chalcogenide and chalcohalide systems and linked with the glass structures.