Determination of Oxygen Nonstoichiometry and Diffusivity in Mixed Conducting Oxides by Oxygen Coulometric Titration. II Oxygen Nonstoichiometry and Defect Model for La0.8Sr0.2CoO3-delta

The oxygen nonstoichiometry of La0.8Sr0.2CoO3-delta has been determined as a function of oxygen partial pressure and temperature using a high-temperature coulometric titration cell. For each measured value of the oxygen chemical potential, the oxygen nonstoichiometry is found to be nearly independent of temperature. The equilibrium partial energy and entropy associated with oxygen incorporation have been determined as a function of oxygen nonstoichiometry and temperature. The results are interpreted in terms of a model in which it is assumed that conduction electrons, created during vacancy formation, gradually fill electron states in a wide electron band. A new relation between vacancy concentration, temperature, and oxygen partial pressure has been formulated which does not have the familiar appearance of a mass action type of equation

Uncoupled Hartree-Fock calculations of the polarizability and hyperpolarizabilities of nitrophenols

The polarizability and hyperpolarizabilities of nitrophenols as model compounds for studying nonlinear optics have been investigated at the Hartree-Fock level of approximation by means of the Dalgarno Uncoupled Hartree-Fock (DUHF) or Sum Over Orbitals (SOO) method. The additive character and the charge transfer effects in α,β,γ and have been analyzed in terms of the δ and π molecular orbital contributions, the contribution of the individual π molecular orbitals, and the contribution of the highest occupied and the lowest unoccupied\ud molecular orbitals. Within the SOO approach, the reliability of the Two-Level Model has been tested and the influence of the rotation of the nitro group and of the presence of the intramolecular hydrogen bonding in ortho-nitrophenol have been studied. The results show that the present method is a reliable and efficient tool for the prediction of trends in the molecular polarizability and hyperpolarizabilities of large molecule

Determination of oxygen nonstoichiometry and diffusivity in mixed conducting oxides by oxygen Coulometric titration

Oxygen coulometric titration has been applied to measure chemical diffusion in La0.8Sr0.2CoO3-δ between 700 and 1000°C. The transient current response to a potentiostatic step has been transformed from the time domain to the frequency domain. The equivalent circuit used to fit the resulting impedance data contains the element that describes the finite-length diffusion of oxygen into the sample specimen. Other elements included are the gas-phase capacitance and the sum of the gas-phase diffusion resistance and that associated with the limited surface exchange kinetics of the sample. The chemical diffusion coefficient of perovskite La0.8Sr0.2CoO3-δ has been determined as a function of temperature and oxygen partial pressure. Its value can be represented by ~D (cm2/s) = 5.91 x exp [(-135 kJ/mol)/RT], and turns out to be practically independent of oxygen partial pressure in the range 10-2 - 0.209 bar

Thermodynamic Quantities and Defect Structure of La0.6Sr0.4Co1−yFeyO3−δ(y=0–0.6) from High-Temperature Coulometric Titration Experiments

The partial energies and entropies of O2in perovskite-type oxides La0.6Sr0.4Co1−yFeyO3−δ(y=0, 0.1, 0.25, 0.4, 0.6) were determined as a function of nonstoichiometryδby coulometric titration of oxygen in the temperature range 650–950°C. An absolute reference value ofδwas obtained by thermogravimetry in air. The nonstoichiometry at a given oxygen pressure and temperature decreases with iron contenty. At low nonstoichiometries the oxygen chemical potential decreases withδ. The observed behavior can be interpreted by assuming random distribution of oxygen vacancies, an electronic structure with both localized donor states on Fe, and a partially filled itinerant electron band, of which the density of states at the Fermi level scales with the Co content. The energy of the Fe states is close to the energy at the Fermi level in the conduction band. The observed trends of the thermodynamic quantities can be interpreted in terms of the itinerant electron model only when the iron content is small. At high values ofδthe chemical potential of O2becomes constant, indicating partial decomposition of the perovskite phase. The maximum value ofδat which the compositions are single-phase increases with temperature

Thermodynamic quantities and defect structure of La0.6St0.4Co1-yFeyO3-d (y=0-0.6) from high-temperature Coulometric titration experiments

The partial energies and entropies of O2in perovskite-type oxides La0.6Sr0.4Co1−yFeyO3−δ(y=0, 0.1, 0.25, 0.4, 0.6) were determined as a function of nonstoichiometryδby coulometric titration of oxygen in the temperature range 650–950°C. An absolute reference value ofδwas obtained by thermogravimetry in air. The nonstoichiometry at a given oxygen pressure and temperature decreases with iron contenty. At low nonstoichiometries the oxygen chemical potential decreases withδ. The observed behavior can be interpreted by assuming random distribution of oxygen vacancies, an electronic structure with both localized donor states on Fe, and a partially filled itinerant electron band, of which the density of states at the Fermi level scales with the Co content. The energy of the Fe states is close to the energy at the Fermi level in the conduction band. The observed trends of the thermodynamic quantities can be interpreted in terms of the itinerant electron model only when the iron content is small. At high values ofδthe chemical potential of O2becomes constant, indicating partial decomposition of the perovskite phase. The maximum value ofδat which the compositions are single-phase increases with temperature

Electric Device with Nanowires Comprising a Phase Change Material

The method according to the invention is directed to manufacturing an electric device ( 100 ) according to the invention, having a body ( 102 ) with a resistor comprising a phase change material being changeable between a first phase and a second phase, the resistor having a first electrical resistance when the phase change material is in the first phase, and a second electrical resistance different from the first electrical resistance when the phase change material is in the second phase. The resistor is a nanowire (NW) electrically connecting a first conductor ( 172, 120 ) and a second conductor ( 108, 121 ).; The method comprises the step of providing a body ( 102 ) having the first conductor ( 172, 120 ), providing the first conductor ( 172, 120 ) with the nanowire (NW) thereby electrically connecting the nanowire (NW) and the first conductor ( 172, 120 ), and providing the nanowire (NW) with the second conductor ( 108, 121 ) thereby electrically connecting the nanowire (NW) and the second conductor ( 108, 121 )

Chemical diffusion and oxygen exchange of La0.6Sr0.4Co0.6Fe0.4O3-d

The transport parameters of La0.6Sr0.4Co0.6Fe0.4O3−δ were determined by electrical conductivity relaxation and high temperature coulometric titration experiments. The experimental response curves were analyzed in the frequency domain. The results obtained by both methods were in good agreement. The chemical diffusion coefficients measured at temperatures of 923–1255 K and oxygen partial pressures of 0.03–1 bar O2, vary between 10−6–5×10−5 cm2 s−1. The experimental activation energies are in the range 95–117 kJ mol−1. At oxygen partial pressures below 0.03 bar O2 the re-equilibration process is completely governed by the rate of oxygen exchange at the interface. The surface exchange coefficients were determined by conductivity relaxation experiments at temperatures of 1000–1285 K and oxygen pressures of 10−4–0.1 bar O2. The activation energy is about 60–70 kJ mol−1. The exchange coefficients are almost proportional to the oxygen pressure. Treatment of the surface in a nitric acid solution for several hours increases the surface exchange rates by factors of 3–5