Electronic conductivity, oxygen permeability and thermal expansion of Sr0.7Ce0.3Mn1 — xAlxO3 — d

Abstract

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.