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

摘要

Perovskite-type oxides La_(1-a)A_aM_(1-b)B_bO_(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 condtions 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 deg 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 deg 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.