Electronic conduction and stability of solid electrolytes based on lanthanum gallates

摘要

The electronic conductivity of some Sr- and Mg-doped lanthanum gallates was measured as a function of the oxygen activity in the p(O2) range of about 10(1)-10(-17) bar using the Hebb-Wagner polarization technique. The investigated compositions were La0.8Sr0.2Ga1-xMgyO3-delta with y=0.15, 0.2, (La0.8Sr0.2)(0.95)Ga0.8Mg0.2O3-delta (LSGM19/20), and the Nd-doped (La0.9Nd0.1)(0.8)Sr0.2Ga0.8Mg0.2O3-delta (LNSGM). Sintered dense pellets of the samples were contacted with glass encapsulated ion-blocking Pt or An microcontacts in pure N-2 atmosphere and a Cu2O/CuO reference electrode. The temperatures ranged between 600 and 750 degreesC. For p(O2)>10(-8) bar, all samples showed p-type conductivity with the expected dependence sigma(h) proportional to p(O2)(1/4) and a weak temperature influence. For p(O2)<10(-12) bar, n-type conduction was found which, however, did not give a Corresponding a sigma(e)p(O2)(-1/4) dependence. Instead, the electronic conductivity approached a limiting value below about p(O2)=10(-15) bar. This result and the observation of an additional irreversible current drift after cathodic polarization for long times suggested a degradation of the materials in the low p(O2) range. This was most probably caused by the loss of Ga2O and/or by the formation of PtGax-alloys. Both effects can explain the observed limitation of the electron concentration in the n-type range. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 21]