Effect of temperature and dopant concentration on the conductivity of samaria-doped ceria electrolyte

The conductivity, σ, of a samaria-doped ceria electrolyte is studied as a function of temperature and dopant concentration, x, which was from 5 to 30 mol%. It is shown that a maximum in σ versus x corresponds to a minimum in activation energy. It is found that the conductivity is completely due to oxygen vacancy conduction. The conductivity increases with increasing samaria doping and reaches a maximum for (CeO₂)_0.8(SmO_1.5)_0.2, which has a conductivity of 5.6×10^–1 S/cm at 800 °C. A curvature at T=T _c, the critical temperature, has been observed in the Arrhenius plot. This phenomenon may be explained by a model which proposed that, below T _c, nucleation of mobile oxygen vacancies into ordered clusters occurs, and, above T _c, all oxygen vacancies appear to be mobile without interaction with dopant cation. In addition, the composition dependences of both the critical temperature and the trapping energy are consistent with that of the activation energy. Electronic Publication     

Electric properties of solid solutions based on strontium tantalate with perovskite-type structure. Protonic conductivity

Conductivity of the Sr_{6 − 2x} Ta_{2 + 2x} O_{11 + 3x} (0 ≤ x ≤ 0.33) solid solutions with the cryolite structure was studied in the atmosphere with a high content of water vapors under temperature and oxygen activity variation in the gas phase. Appearance of the protonic conductivity component was proved at the temperatures below 700°C. It was found that protonic conductivity increases at a decrease in parameter x in the composition series, which is due to an increase of both the concentration of protonic defects formed in the structure and of their mobility. In the case of compositions with x < 0.15 at the temperatures below 550°C, the protonic transport becomes predominant.     

470—The proton pump at work: Part I. The basic concept of excess proton/defect proton translocation

The Nagle-Morowitz proton pump, which is based on proton transport in water and ice, is shown to be inapplicable to weakly H-bonded proton transport systems. It is demonstrated that in weakly or non H-bonded systems protons can migrate either as excess protons H using a high-lying proton conduction band or as defect protons H′ using intermediate energy levels. As H? the protons act as positive charge carriers endowed with a very high mobility. As H′ they act as negative charge carriers. The H′ transport mechanism involves thermally activated proton tunneling. Owing to the very large mobility differences between H? and H′, > 10⁶, very high potentials can be self-generated in any situation which creates a concentration gradient. Proton conductivity data on inorganic model compounds are presented. Applying these results to proton transport across biomembranes, transmembrane potentials U_m, acidification Δ pH and transient phenomena can be explained as result of H? and H′ translocation.     

BaCe0.8Ho0.2O3-a陶瓷的性质与应用

Ceramic BaCe0.8Ho0.2O3-α with orthorhombic perovskite structure was prepared by conventional solid state reaction, and its conductivity and ionic transport number were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 600-1000 ℃ in wet hydrogen and wet air, respectively. Using the ceramics as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at temperature from 600-1000 ℃ was examined. The results indicate that the specimen was a pure protonic conductor with the protonic transport number of 1 at temperature from 600-900 ℃ in wet hydrogen, a mixed conductor of proton and electron with the protonic transport number of 0.99 at 1000 ℃. The electronic conduction could be neglected in this case, thus the total conductivity in wet hydrogen was approximately regarded as protonic conductivity. In wet air, the specimen was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.01-0.09, and the oxide-ionic transport numbers were 0.27-0.32. The oxide ionic conductivity was increased with the increase of temperature, but the protonic conductivity displayed a maximum at 900 ℃, due to the combined increase in mobility and depletion of the carriers. The fuel cell could work stably. At 1000 ℃, the maximum short-circuit current density and power output density were 346 mA/cm^2 and 80 mW/cm^2, respectively.     

Thermal stability and crystallization kinetics in superionic glasses using electrical conductivity–temperature cycles

The present work demonstrates application of electrical conductivity (σ)–temperature (T) cycles to investigate thermal properties viz., crystallization and glass transition kinetics in AgI–Ag₂O–V₂O₅–MoO₃ superionic glasses. The σ–T cycles are carefully performed at various heating rates, viz., 0.5, 1, 3, 5, and 7 K/min. The conductivity in Ag⁺ ion conducting glasses exhibit anomalous deviation from Arrhenius behavior near glass transition temperature (T _g) followed by a drastic fall at crystallization (T _c). The temperature corresponding to maximum rate of crystallization (T _p) is obtained from the derivative of σ–1/T plots. With increasing heating rates, the characteristic temperatures (T _g, T _p) are found to be shifting monotonically toward higher temperatures. Thus, activation energy of structural relaxation E _s, crystallization E _c and other thermal stability parameters have been obtained from σ–T cycles using Kissinger equation and Moynihan formulation. For a comparative study, these kinetics parameters have also been calculated from differential scanning calorimetry plots. The parameters obtained from both the methods are found to be comparable within experimental error.     

Microstructure and protonic conductivity of H3PO4‐doped polyethylenimine–siloxane chemically covalently organic–inorganic hybrids

The chemically covalent polyethylenimine–siloxane hybrids doped with various amounts of ortho‐phosphoric acid (H₃PO₄) were prepared and characterized by FTIR, DSC, TGA, and solid‐state NMR spectra. The protonic conduction behavior of these materials was also investigated by means of impedance measurements. These observations indicate that the hydrogen bonding and protonic interactions exist between the dopant H₃PO₄ and the hybrid host, resulting in an increase in T _g of polyethylenimine segments. These hybrids are thermally stable up to 200 °C from TGA analysis. Conductivity studies show an Arrhenius behavior characteristic and the Grotthus‐like proton conduction, and a high conductivity of 10^?2–10^?3 S cm^?1 at 110 °C in dry atmosphere for the hybrid membrane with H₃PO₄/EI of 0.5. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2135–2144, 2006     

Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

Water proton spin-lattice relaxation behaviour in heterogeneous biological systems

The water proton spin-lattice relaxation rate has been measured for a condensed 50% deuterated erythrocyte water system. Nuclear relaxation data, obtained in non-selective and selective modes, indicate that cross relaxation between erythrocyte and water protons occurs. The observed selective relaxation enhancement is interpreted in terms of intermolecular nuclear interactions modulated by motions which satisfy the ω_oT_c > 1 condition. Selective relaxation rates are here proposed to be more sensitive to interface characteristics than the non-selective ones.     

Synthesis, Characterization, and Catalytic Activity of Rh(I) Complexes with (S)-BINAPO, an Axially Chiral Inducer Capable of Hemilabile P,O-Heterobidentate Coordination

Summary.  The reaction of dinuclear rhodium(I) derivatives of the formula [Rh(DIOL)X]₂ with the axially chiral phosphinyl phosphane 2-(diphenylphosphinyl)-2′-(diphenylphosphanyl)-1,1′-binaphthalene ((S)-BINAPO, 1) leads to the formation of cationic complexes [(BINAPO)Rh(DIOL)]⁺ where the ligand (S)-BINAPO consistently displays a P,O-chelate coordination which is mantained even in solvents of fair polarity. The mononuclear rhodium(I) complexes (S)-2-diphenylphosphanyl-2′-diphenylphosphinyl-1,1′-binaphthalene-(1,5-cyclooctadiene) rhodium tetrafluoroborate (3b) and (S)-2-diphenylphosphanyl-2′-diphenylphosphinyl-1,1′-binaphthalene-(1,4-norbornadiene) rhodium tetrafluoroborate (3c) with 1,5-cyclooctadiene (COD) and 2,5-norbornadiene (NBD) as the diolefin were isolated and characterized. Both show a fluxional behaviour in solution which is due to the mobility of the diolefin rather than to a displacement-recombination of the oxygenated arm of the ligand. The mobility of the 1,4-norbornadiene ligand in 3c is extremely pronounced and the coordinated diolefin flexibility could be frozen only at about 200 K. These complexes are active but poorly stereoselective catalysts for the hydrogenation, hydroboration, and hydroformylation of alkenes. Received June 16, 2000. Accepted (revised) July 24, 2000     

Unexpected proton spin‐lattice relaxation in the solutions of polyolefin and tetrachloroethane

‘Unexpected’ proton spin‐lattice relaxation (T₁) times are reported for the solutions of poly(ethylene‐co‐1‐octene) and tetrachloroethane‐d₂. For the residual protons of the deuterated solvent and the methyl and vinyl protons at the polymer chain ends, their T₁ relaxation times vary significantly with both the polymer concentration and molecular weight over a wide range. The T₁s also decrease with increasing temperature at relative high temperatures. Such behaviors are in contrast to most reported polymer solutions in which the T₁ has nearly no concentration or molecular weight dependence in the dilute and semi‐dilute regime, and normal dependence on temperature. Further investigation revealed that the paramagnetic oxygen effect did shorten the measured proton T₁s, but cannot account for the unexpected T₁ dependences. Spin rotation is proposed to provide a reasonable explanation. Copyright © 2010 John Wiley & Sons, Ltd.     

Proton transport through hydrated chitosan‐based polymer membranes under electric fields

Proton transport is essential in many areas of chemistry and biology and is especially important in the fields of proton exchange membrane fuel cells and biocompatible, protonic semiconductors. These devices make use of membranes to control the flow of protons for either the generation of energy or to more closely couple electronics and biology. In the present study, we make use of ab initio molecular dynamics simulations, including the effect of applied electric fields, to gain atomistic insight into the intrinsic conductivity of chitosan‐based polymers and demonstrate that chitosan does not act as a significant source of friction for the transport of protons while increasing the number of free ions. Published 2017.^? J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1103–1109     

Gelation Studies, 3

Summary: The sol‐gel transition of one thermoreversible gelling mixture made of xanthan gum and locust bean gum has been studied by using in situ time‐resolved dynamic light scattering (DLS) and measuring the spin‐lattice relaxation time T₁ of several protons. A critical dynamical behavior was observed near the sol‐gel transition, which is characterized by the presence of power‐law spectra over four decades of the delay time in the time‐intensity correlation function g₂(t)−1 ∼ t^−μ at 48 °C. The increase in T₁ with increasing temperature becomes steeper at 50 °C indicating a significant change in the local mobility of one anomeric proton of the xanthan side chain and the anomeric protons of the locust bean gum mannose backbone.

Temperature dependence of the spin‐lattice relaxation time T₁ for the equatorial anomeric proton of the mannopyranosic unit located next to the main chain of the xanthan.     

High resolution 1H-NMR relaxation study of polyisobutylene in solution

From the temperature dependence of integrated intensities and from line widths in high-resolution ¹H-NMR spectra, the relaxation times T₁ and T₂ of protons in CH₂ and CH₃ groups of polyisobutylene in CCl₄ solution have been determined. Although the relaxation time T₁ of methylene protons is determined mainly by intragroup interactions, intergroup interactions of two methyl groups from each two consecutive monomer units were found to contribute considerably to T₁ of methyl protons. The Structure and mobility of polyisobutylene (PIB) molecules in solution is discussed on the basis of the relaxation time data.     

Protonic conduction and the Néel temperature in deuterated ammonium dihydrogen arsenate

The conductivity of antiferroelectric ND₄D₂AsO₄ single crystals has been measured as a function of temperature, especially near the Néel temperature. At the Néel temperature the conductivity shows a vertical decrease to a lower value indicating that the mechanism of conduction is connected to the shift of the protons during the phase transition. This conductivity mechanism in potassium and ammonium dihydrogen phosphates and arsenates has been previously proposed to include proton motion along hydrogen bonds and proton jumps across the phosphate or arsenate tetrahedra. The jump activation energy for proton mobility in ND₄D₂AsO₄ is found to be 10.5 kcal/mole and the room temperature conductivity is 9.91 × 10^?10 ohm^?1 cm^?1.     

Direct current conduction in ammonium perchlorate single crystals

The dc electrical conductivity of pure and doped ammonium perchlorate (AP) has been studied in two different crystal orientations, with the electric field applied perpendicularly to either (001) or (210) planes. The conductivity along the direction of the c axis was found to be lower than that normal to (210) by a factor of 5 to 10. The dc electrical conductivity of AP is decreased by Pb²⁺ ions but increased by SO^2?₄ and CrO^2?₄ ions. The conductivity of pure AP and of Pb²⁺-doped AP displays two regions with activation energies for conduction of 0.56 and 0.87 eV, respectively. The conductivity of the anion-doped crystals has a single activation energy, 0.66 eV for SO^2?₄ and 0.72 eV for CrO^2?₄. Exposure to ammonia enhances the conductivity of pure AP. A proton conduction mechanism is proposed that takes due regard of the structure of AP. The effect of the various additives on the conductivity are attributed to their influences on the formation of charge-carrying protons.     

A study of the phase transitions and proton dynamics of the superprotonic conductor Cs5H3(SO4)4·0.5H2O single crystal with H and Cs nuclear magnetic resonance

The phase transitions and proton dynamics of Cs₅H₃(SO₄)₄·0.5H₂O single crystals were studied by measuring the NMR line shape, the spin-lattice relaxation time, T₁, and the spin-spin relaxation time, T₂, of the ¹H and ¹³³Cs nuclei. The “acid” protons and the “water” protons in Cs₅H₃(SO₄)₄·0.5H₂O were distinguished. The loss of water protons was observed above T_C1, whereas the content of water protons was found to recover above T_C2. Therefore, the water protons play a special role in the stability of the superprotonic phase at high temperatures. The mechanism of fast proton conduction was found to consist of hydrogen-bond proton transfer involving the breakage of the weak part of the hydrogen bond and the formation of a new hydrogen bond. Thus, these structural phase transitions probably involve significant reorientation of the SO₄ tetrahedra and dynamical disorder of the hydrogen bonds between them.     

Identification of proton type in concentrated sweet solutions by pulsed NMR analysis

The spin-spin proton relaxation times T₂ of concentrated sucrose, maltose,D-glucose andL-proline solutions were determined using a Bruker Minispec NMR Spectrometer. Log spin echo amplitude decay curves were also determined and their non-linear nature allowed the proportions of different proton types to be calculated. These were in agreement with the theoretical proportions of ring (non-exchangeable protons), solute hydroxyl protons and water protons in the simple sugar molecules. A deuteration experiment confirmed that only non-exchangeable ring protons remained.     

A model for dynamic relaxations in amorphous polymers. II. Extensions and generalizations of formalism and application to poly(methacrylates)

Extensions and generalizations of a new model for the dynamic relaxations in amorphous polymers, and its application to the poly(methacrylates), will be presented. The sizes of moving subunits will be extrapolated for the β and γ relaxations in several poly(methacrylates), by working backward from the relaxation temperatures (T_r) observed at frequencies of 1 to 100 Hz to subunits giving T_cs comparable to those T_rs. A general form will be proposed for activation energy distributions; and used to derive relaxation time distributions satisfying the experimental trends. The good agreement between the calculated T_c and the T_r observed dynamically at frequencies of 1 to 100 Hz will be shown to result from the nature of these distributions. The loss peak observed at very low temperatures by isochronal sweeps at very low frequencies is therefore caused by the dissipation of applied energy in localized domains. At sweep frequencies of 1 to 100 Hz, T_r ≈ T_c, and energy dissipation begins to take place over regions spanning the entire polymer. This delocalization of the energy dissipation is relevant to the effects of molecular level factors on many mechanical and thermodynamic properties of amorphous polymers. The effects of activation entropy and of dynamic excess entropy will be shown to be small in magnitude but important in terms of fully understanding relaxation behavior. Physical aging will be shown to result in a slight increase in the calculated characteristic temperatures. Finally, it will be shown that the relaxation behavior of the moduli and the compliances share some important common features with many other physical phenomena of seemingly very different nature.     

A Tetradentate Phosphonate Ligand-based Ni-MOF as a Support for Designing High-performance Proton-conducting Materials

Developing a robust metal-organic framework (MOF) which facilitates proton hopping along the pore channels is very demanding in the context of fabricating an efficient proton-conducting membrane for fuel cells. Herein, we report the synthesis of a novel tetradentate aromatic phosphonate ligand H₈L (L=tetraphenylethylene tetraphosphonic acid) based Ni-MOF, whose crystal structure has been solved from single-crystal X-ray diffraction. Ni-MOF [Ni₂(H₄L)(H₂O)₉(C₂H₇SO)(C₂H₇NCO)] displays a monoclinic crystal structure with a space group of P 2₁/c, a=11.887 Å, b=34.148 Å, c=11.131 Å, α= γ =90°, β=103.374°, where a nickel-hexahydrate moiety located inside the void space of the framework through several H-bonding interactions. Upon treatment of the Ni-MOF in different pH media as well as solvents, the framework remained unaltered, suggesting the presence of strong H-bonding interactions in the framework. High framework stability of Ni-MOF bearing H-bonding interactions motivated us to explore this metal-organic framework material as proton-conducting medium after external proton doping. Due to the presence of a large number of H-bonding interactions and the presence of water molecules in the framework we have carried out the doping of organic p-toluenesulfonic acid (PTSA) and inorganic sulphuric acid (SA) in this Ni-MOF and observed high proton conductivity of 5.28×10⁻² S cm⁻¹ at 90 °C and 98% relative humidity for the SA-doped material. Enhancement of proton conductivity by proton doping under humid conditions suggested a very promising feature of this Ni-MOF.     

DSC Research on Critical Temperature in Thermal Explosion Synthesis Reaction Ti+3Al→TiAl3

The critical furnace chamber temperature (T′_ign) of the thermal explosion synthesis reaction Ti+3Al→TiAl₃ is studied by isothermal and non-isothermal DSC. The reaction product is characterized by using the X-ray powder diffraction. The value of T′_ign is between 740 and 745°C obtained from the isothermal DSC observations, and 729°C obtained from non-isothermal DSC curves. It shows that these two values have a good consistency. With the help of the apparent activation energy of the reaction obtained by Friedman method and the value of T′_ign0 by the multiple linear regression of the T′_igns at different heating rates (β), the critical temperature (T _b) of thermal explosion for Ti–75at%Al mixture is estimated to be 785°C. This revised version was published online in August 2006 with corrections to the Cover Date.