abstract
Iron incorporation into lanthanum alurninate-based solid electrolyte leads to increasing oxygen ionic and p-type electronic conductivities. The oxygen ion transference numbers of perovskite-type La(0.90)Sr(0.10)Al(0.85-x)FexMg(0.15)O(3-delta) (x = 0.2-0.4), determined by faradaic efficiency measurements in air, vary from 6.9 x 10(-4) to 1.6 x 10(-2) at 1073-1223 K, increasing with temperature and decreasing when iron content increases. In order to study the behavior of transition metal cations dissolved in a lattice of cations with stable oxidation state, the total conductivity and Seebeck coefficient of La(0.90)Sr(0.10)Al(0.65)Fe(0.20)Mg(0.15)O(3-delta) were measured at 1073-1223 K in the oxygen partial pressure range from 10(-20) to 0.5 atm. The p-type electronic conduction dominating under oxidizing conditions, with hole mobility activation energy of 15 kJ mol(-1), occurs via a small-polaron mechanism. Reducing oxygen pressure results in increasing ionic conduction, which becomes predominant at (P)(O(2)) lower than 10(-10) atm. The activation energy for ionic transport, 87-107 kJ mol(-1), decreases with reducing (P)(O(2)) due to a decreasing contribution of the vacancy formation enthalpy. Contrary to the Fe-substituted aluminates, dense ceramics of La(Sr)AI(Mg,M)O(3-delta) (M = Co, Ni) cannot be obtained under atmospheric oxygen pressure due to La(2)MO(4)-based phase segregation in the course of sintering at temperatures above 1400 K. (c) 2004 Elsevier SAS. All rights reserved.
keywords
ELECTRICAL-CONDUCTIVITY; ELECTRONIC CONDUCTIVITY; THERMOELECTRIC-POWER; REDUCING ATMOSPHERE; OXYGEN PERMEABILITY; SYNGAS PRODUCTION; OXIDE; CO; PEROVSKITES; CR
subject category
Chemistry; Physics
authors
Tsipis, EV; Kharton, V; Vyshatko, N; Frade, JR; Marques, FMB
our authors
Fernando Manuel Bico Marques
Full professor
Jorge Ribeiro Frade
Retired Professor