Ionic/electronic mixed conduction relations in perovskite-type oxides by defect structure

Perovskite-type oxides La(1-a)A(a)M(1-b)B(b)O(3-x) with A = Sr(2+), Ln(3+), Ce(4+) and M = Fe, Co, Ga; B = Co, Fe, Mg were prepared in the concentration range a = 0.1 to 1 mol and b = 0.1 to 0.5 mol. Additionally, A-substoichiometric compositions were prepared. Preparation conditions for monophase materials and structure types of the perovskite were determined by X-ray investigation. The electrical conductivity as a function of pO(2) in the range 10(5) > pO(2) > 10(-14) Pa and temperature (500 to 1000 degrees C) was measured on ceramic shapes by a dc four-point technique in combination with solid electrolyte coulometry. The ionic part of conductivity in mixed conductors was determined by oxygen permeation measurements. The II-III-perovskites Sr(Co, Fe)O(3-x) in their stabilized form are excellent mixed conductors (maximum 500 S cm(-1) at 400 degrees C) and have up to 2 orders of magnitude higher oxygen ionic conductivity than the preferred III-III-perovskite La(Sr)Mn(Co)O(3-x). The oxygen ionic conductivity of the electrolyte La(Sr)Ga(Mg)O(3-x), was increased by doping with 0.1 mol Co. By applying higher Co or Fe doping concentrations the lanthanum gallate, becomes a mixed conductor. (C) 1999 Elsevier Science Limited. All rights reserved.