Perovskite-related oxide materials for oxygen-permeable electrochemical membrans

This brief review is focused on the studies of mixed ionic-electronic conductors on the basis of lanthanum gallate doped with transition metal cations in the В sublattice. The substitution of gallium with iron, cobalt or nickel results in greater electronic conductivity, simultaneously keeping high level of the oxy-gen ionic transport. In particular, La0 90Sr0 10Ga0 65Ni0 20Mg0 1503d perovskite exhib-its attractive oxygen permeability, which is quite similar to that of La2Ni04- and (La,Sr)Co03-based phases The combination of appropriate transport and thermomechanical properties with sufficiently high thermodynamic stability en-ables to use Ni- or Fe-substituted LaGa03-based mixed conductors for the mem-brane electrocatalytic reactors for partial oxidation of light hydrocarbons

Perovskite-related oxide materials for oxygen-permeable electrochemical membrans

This brief review is focused on the studies of mixed ionic-electronic conductors on the basis of lanthanum gallate doped with transition metal cations in the В sublattice. The substitution of gallium with iron, cobalt or nickel results in greater electronic conductivity, simultaneously keeping high level of the oxy-gen ionic transport. In particular, La0 90Sr0 10Ga0 65Ni0 20Mg0 1503d perovskite exhib-its attractive oxygen permeability, which is quite similar to that of La2Ni04- and (La,Sr)Co03-based phases The combination of appropriate transport and thermomechanical properties with sufficiently high thermodynamic stability en-ables to use Ni- or Fe-substituted LaGa03-based mixed conductors for the mem-brane electrocatalytic reactors for partial oxidation of light hydrocarbons

Электронная проводимость, кислородная проницаемостьи термическое расширение Sr0.7Ce0.3Mn1 — xAlxO3 — d

The maximum solubility o f aluminum cations in the perovskite lattice o f 8 г0 7 СеозМп1_гА1гОз_л is approximately 15%. The incorporation o f Al3+ increases oxygen ionic transport due to increasing oxygen nonstoichiometry, and decreases the tetragonal unit cell volume and thermal expansion at temperatures above 600 С. The total conductivity o f 5го7 Сео.зМп|_(А1гОз_л (дг = 0-0.2), predominantly electronic, decreases with aluminum additions and has an activation energy o f 10.2-10.9 kJ/mol at 350-850 C. Analysis o f the electronic conduction and Seebeck coefficient o f Sro.7 Ceo.3Mno.9 Alo 1 0 3_*, measured in the oxygen partial pressure range from 10 IH to 0.5 atm at 700-950 C, revealed trends characteristic o f broad-band semiconductors, such as temperature-independent mobility. The temperature dependence o f the charge carrier concentration is weak, but exhibits a tendency to thermal excitation, whilst oxygen losses from the lattice have an opposite effect. The role o f the latter factor becomes significant at temperatures above 800 С and on reducing p (0 2) below 10- 4 to 10 2 atm. The oxygen permeability o f dense Sro^CeojMni ..гА1,Оз_* (* = 0 - 0 .2 ) membranes, limited by both bulk ionic conduction and surface exchange, is substantially higher than that o f (La, Sr)Mn03-based materials used for solid oxide fuel cell cathodes. The average thermal expansion coefficients o f Sro^CeojMni.jAUCb.j ceramics in air are (10.8-11.8) x 10~6K c 2005 Elsevier Ltd. All rights reserved

Oxygen transport in La2NiO4 + [delta]: Assessment of surface limitations and multilayer membrane architectures

http://www.sciencedirect.com/science/article/B6TY4-4VMBNT9-3/2/2c6a74f1bb2f51b7b9503333d1045f0

Электронная проводимость, кислородная проницаемостьи термическое расширение Sr0.7Ce0.3Mn1 — xAlxO3 — d

The maximum solubility o f aluminum cations in the perovskite lattice o f 8 г0 7 СеозМп1_гА1гОз_л is approximately 15%. The incorporation o f Al3+ increases oxygen ionic transport due to increasing oxygen nonstoichiometry, and decreases the tetragonal unit cell volume and thermal expansion at temperatures above 600 С. The total conductivity o f 5го7 Сео.зМп|_(А1гОз_л (дг = 0-0.2), predominantly electronic, decreases with aluminum additions and has an activation energy o f 10.2-10.9 kJ/mol at 350-850 C. Analysis o f the electronic conduction and Seebeck coefficient o f Sro.7 Ceo.3Mno.9 Alo 1 0 3_*, measured in the oxygen partial pressure range from 10 IH to 0.5 atm at 700-950 C, revealed trends characteristic o f broad-band semiconductors, such as temperature-independent mobility. The temperature dependence o f the charge carrier concentration is weak, but exhibits a tendency to thermal excitation, whilst oxygen losses from the lattice have an opposite effect. The role o f the latter factor becomes significant at temperatures above 800 С and on reducing p (0 2) below 10- 4 to 10 2 atm. The oxygen permeability o f dense Sro^CeojMni ..гА1,Оз_* (* = 0 - 0 .2 ) membranes, limited by both bulk ionic conduction and surface exchange, is substantially higher than that o f (La, Sr)Mn03-based materials used for solid oxide fuel cell cathodes. The average thermal expansion coefficients o f Sro^CeojMni.jAUCb.j ceramics in air are (10.8-11.8) x 10~6K c 2005 Elsevier Ltd. All rights reserved

Oxygen Nonstoichiometry, Mixed Conductivity, and Mössbauer Spectra of Ln0.5A0.5FeO3−δ (Ln = La−Sm, A = Sr, Ba): Effects of Cation Size

Increasing the difference of the Ln3+ and A2+ cation radii in perovskite-type Ln0.5A0.5FeO3−δ (Ln = La, Pr, Nd, Sm; A = Sr, Ba) results in higher oxygen deficiency and lower oxygen-ionic and p-type electronic conductivities, determined using the oxygen permeation and total conductivity measurements at 973−1223 K. The relationships between the anion transport and A-site cation size mismatch remain essentially similar in air and under reducing conditions when most iron cations become trivalent, thus confirming critical influence of oxygen-vacancy trapping processes induced by the lattice strain. At low temperatures, analogous correlation is also observed for quadrupole splittings derived from the Mssbauer spectra of oxygen-stoichiometric Ln0.5A0.5FeO3. Contrary to the ionic conductivity variations, the role of surface exchange kinetics as a permeation-limiting factor, evaluated from the membrane thickness dependence of oxygen fluxes, tends to decrease on Ba2+ doping and on decreasing Ln3+ size in Ln0.5Sr0.5FeO3−δ series. The n-type electronic conduction and low-p(O2) stability at 1223 K are substantially unaffected by the cation radius mismatch

Mixed conductivity in La(Ga,Mg,Nb)O_3-δ Perovskites

Solid-solution formation has been found in the perovskite-type system LaGa0.85-xMg0.15(Nb0.33Mg0.66)xO3-δ (x = 0 - 0.20). Increasing dopant concentration leads to lower oxygen ionic conductivity and, at temperatures above 1000 K, higher p-type electronic conductivity. Oxygen-ion transference numbers in air were determined to vary in the range 0.78 to 0.96, decreasing with increasing x and temperature. Thermal expansion coefficients of ceramic samples of LaGa0.85-xMg0.15(Nb0.33Mg0.66)xO3-δ were calculated in a temperature range of 300 to 1100 K to be essentially independent of composition, varying in the range (10.0 ± 0.2) x 10-6 K-1. Values of the activation energy for the total electrical conductivity in air are 104-106 kJ/mol in the temperature range 670 - 1000 K and 67 - 76 kJ/mol in the temperature range 1000 - 1200 K. The method of synthesis was found to affect both the symmetry of the perovskite unit cell and phase composition. The presence of second phases led to a dramatic decrease in conductivity.Se ha encontrado la formación de una solución sólida en el sistema LaGa0.85-xMg0.15(Nb0.33Mg0.66)xO3-δ (x = 0 - 0.20). Un aumento de la concentración de dopante lleva a una menor conductividad iónica de oxígeno y a temperaturas superiores a 1000 K, una mayor conductividad electrónica de tipo p. El número de transferencia del ión oxígeno en aire fue determinado y varía en el rango 0.78 a 0.96 disminuyendo con el aumento de x y de la temperatura. El coeficiente de expansión térmico de las muestras cerámicas de LaGa0.85-xMg0.15(Nb0.33Mg0.66)xO3-δ fue calculado en el rango de temperatura de 300 a 1100 k siendo independiente de la composición, y variando en el rango (10.0 ± 0.2) x 10-6 K-1. Los valores de la energía de activación para la conductividad eléctrica total en aire son 104-106 KJ/mol en el rango de temperatura 670-1000 K y 67-76 kJ/mol en el rango de temperaturas 1000-1200 K. Se encontró que el método de síntesis afecta tanto a la simetría de la celda unidad de la red perovskita como a la composición de fases. La presencia de fases secundarias lleva a la disminución dramática de la conductividad

Monoenergetic electronic beam production using dual collinear laser pulses

The production of monoenergetic electron beams by two copropagating ultrashort laser pulses is investigated both by experiment and using particle-in-cell simulations. By proper timing between guiding and driver pulses, a high-amplitude plasma wave is generated and sustained for longer than is possible with either of the laser pulses individually, due to plasma waveguiding of the driver by the guiding pulse. The growth of the plasma wave is inferred by the measurement of monoenergetic electron beams with low divergence that are not measured by using either of the pulses individually. This scheme can be easily implemented and may allow more control of the interaction than is available to the single pulse scheme. © 2008 The American Physical Societ