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

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

Ultrashort pulse filamentation and monoenergetic electron beam production in lwfas

In the experiments reported here, the filamentation of ultrashort laser pulses, due to non-optimal choice of focusing geometry and/or electron number density, has a severely deleterious effect on monoenergetic electron beam production in laser wakefield accelerators. Interactions with relatively small focal spots, w0 < λp/2, and with pulse length cτ λp, incur fragmentation into a large number of low power filaments. These filaments are modulated with a density dependent size of, on average, close to λp. The break-up of the driving pulse results in shorter interaction lengths, compared with larger focal spots, and broad energy-spread electron beams, which are not useful for applications. Filamentation of the pulse occurs because the strongly dynamic focusing (small f-number) of the laser prevents pulse length compression before reaching its minimum spot-size, which results in non-spherical focusing gradients

Ionic conductivity of La(Sr)Ga(Mg,M)O3-delta (M = Ti, Cr, Fe, Co, Ni): effects of transition metal dopants

Oxygen-ion conductivity of the perovskite-type solid solutions (La,Sr)Ga1-zM2O3-delta (M = Ti, Cr, Fe, Co; z = 0-0.20), LaGa(1-y-x)Mg(y)MiO(3-delta) (M = Cr, Fe, Co; y = 0.10-0.20, z = 0.35-0.60) and LaGa1-zNizO3-delta (z = 0.20-0.50) was studied using the techniques of oxygen permeation, Faradaic efficiency, ion-blocking electrode and the e.m.f. of oxygen concentration cells. Oxygen-ion transference numbers vary from 2 x 10(-6) to 0.98 throughout the series and p-type electronic conductivity increases with increasing transition metal content. Substitution of Ga with higher valence cations (Ti, Cr) decreases ionic conductivity whereas small amounts of Fe or Co (similar to 5%) increase ionic conductivity. For higher transition metal contents, lower levels of oxygen-ion conductivity and an increase in the activation energy, E-A, for ionic transport, from 60 (5%-doped) to 230 kJ/mol ( &gt; 40%-doped) are observed. In heavily doped phases, E-A tends to decrease with temperature and, above 1170 K, values are similar to the undoped phase suggesting that an order-disorder transition takes place. Factors affecting the observed ionic conductivity trends are discussed. (C) 2000 Published by Elsevier Science B.V. All rights reserved.</p

The generation of mono-energetic electron beams from ultrashort pulse laser-plasma interactions

The physics of the interaction of high-intensity laser pulses with underdense plasma depends not only on the interaction intensity but also on the laser pulse length. We show experimentally that as intensities are increased beyond 1020 W cm(-2) the peak electron acceleration increases beyond that which can be produced from single stage plasma wave acceleration and it is likely that direct laser acceleration mechanisms begin to play an important role. If, alternatively, the pulse length is reduced such that it approaches the plasma period of a relativistic electron plasma wave, high-power interactions at much lower intensity enable the generation of quasi-mono-energetic beams of relativistic electrons

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