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-z M2O3-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 e fficiency, ion-blocking electrode and the e.m.f. of oxygen concentration ce lls. Oxygen-ion transference numbers vary from 2 x 10(-6) to 0.98 throughou t the series and p-type electronic conductivity increases with increasing t ransition metal content. Substitution of Ga with higher valence cations (Ti , Cr) decreases ionic conductivity whereas small amounts of Fe or Co (simil ar 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 ( > 40% -doped) are observed. In heavily doped phases, E-A tends to decrease with t emperature and, above 1170 K, values are similar to the undoped phase sugge sting that an order-disorder transition takes place. Factors affecting the observed ionic conductivity trends are discussed. (C) 2000 Published by Els evier Science B.V. All rights reserved.