Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1531772 | Materials Science and Engineering: B | 2006 | 9 Pages |
Abstract
The electrical properties of perovskite-type (La0.3Sr0.7)1âyCoO3âδ (y = 0-0.03) and La0.3Sr0.7Co0.8M0.2O3âδ (M = Al, Ga), promising parent materials of dense mixed-conducting membranes for oxygen separation, were studied in the oxygen partial pressure range from 10â14 to 0.5 atm. The steady-state oxygen permeation fluxes through cobaltite ceramics at 973-1223 K are limited by both bulk ionic conductivity and surface exchange kinetics. The substitution of cobalt with Al3+ or Ga3+ increases cubic perovskite unit cell volume, oxygen deficiency and Seebeck coefficient, whereas the thermal expansion, p-type electronic conductivity and oxygen permeability decrease. The creation of A-site cation vacancies, compensated by Co4+ formation, leads to higher p-type electronic conductivity and thermal expansion at temperatures above 700 K, whilst the ionic transport in A-site deficient cobaltite is lower than that in La0.3Sr0.7CoO3âδ. Reducing oxygen pressure down to approximately 10â5 atm results in transition into brownmillerite-type phases having essentially p(O2)-independent electrical properties until decomposition, which occurs at p(O2) values 102 to 104 times higher compared to CoO/Co boundary. The average thermal expansion coefficients of cobaltite ceramics in air are (15.9-19.6) Ã 10â6 Kâ1 at 300-750 K and (27.9-29.7) Ã 10â6 Kâ1 at 750-1240 K.
Keywords
Related Topics
Physical Sciences and Engineering
Materials Science
Electronic, Optical and Magnetic Materials
Authors
V.V. Kharton, E.V. Tsipis, A.A. Yaremchenko, I.P. Marozau, A.P. Viskup, J.R. Frade, E.N. Naumovich,