Abstract
Acceptor-type doping of perovskite-type La 1-x Sr x Ga 0.80-y Mg y M 0.20 O 3-δ (x = 0-0.20, y = 0.15-0.20, M = Fe, Co, Ni) leads to significant enhancement of ionic conductivity and oxygen permeability due to increasing oxygen vacancy concentration. The increase in strontium and magnesium content is accompanied, however, with increasing role of surface exchange kinetics as permeation-limiting factor. At temperatures below 1223 K, the oxygen permeation fluxes through La(Sr)Ga(Mg,M)O 3-δ membranes with thickness less than 1.5 mm are predominantly limited by the exchange rates at membrane surface. The oxygen transport in transition metal-containing La(Sr)Ga(Mg)O 3-δ ceramics increase in the sequence Co < Fe < Ni. The ionic conduction in these phases is, however, lower than that in the parent compounds, La 1-x Sr x Ga 1-y Mg y O 3-δ . The highest level of oxygen permeation, comparable to that of La(Sr)Fe(Co)O 3 - and La 2 NiO 4 -based phases, is observed for La 0.90 Sr 0.10 Ga 0.65 Mg 0.15 Ni 0.20 O 3-δ membranes. The average thermal expansion coefficients of La(Sr)Ga(Mg,M)O 3-δ ceramics in air are in range (11.6-18.4) x 10 -6 K -1 at 373-1273 K. Doping of LaGa 0.65 Mg 0.15 Ni 0.20 O 3-δ with praseodymium results in moderate increase of the permeation fluxes, lower thermal expansion and an improved phase stability in reducing environments.
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