Defect chemistry and oxygen transport of (La 0.6Sr 0.4 − xM x) 0.99Co 0.2Fe 0.8O 3 − δ, M = Ca ( x = 0.05, 0.1), Ba ( x = 0.1, 0.2), Sr : Part II: Oxygen transport

Abstract

This paper is the second part of a two part series, where the effects of varying the A-site dopant on the defect chemistry and transport properties of the materials (La 0.6Sr 0.4 − x M x ) 0.99Co 0.2Fe 0.8O 3 − δ , M = Sr, Ca ( x = 0.05, 0.1), Ba ( x = 0.1, 0.2) (LSMFC) have been investigated. In part I, the findings on the defect chemistry were reported, while the oxygen transport properties are reported here in part II. In the investigated material series, the amount of divalent dopant has been kept constant, while Sr ions have been substituted with Ca ions (smaller ionic radius) or Ba ions (larger ionic radius). The size difference induces different strains into the crystal structure in each composition. The possibility of simple relationships between various crystal strain parameters and the transport properties were analyzed. Oxygen pump controlled permeation experiments and a surface sensitive electrolyte probe were used to extract the permeability and surface resistance, r s. The highest permeability was found for (La 0.6Sr 0.3Ca 0.1) 0.99Co 0.2Fe 0.8O 3 − δ . The apparent activation energy of the permeability was 78 kJ/mol. The inverse surface resistance, r s − 1 , also had an activated behavior with an activation energy close to 180 kJ/mol for most of the materials. A reversible transition to an abnormally low r s was found in (La 0.6Sr 0.3Ca 0.1) 0.99Co 0.2Fe 0.8O 3 − δ at T > 1223 K.