Equilibrium of point defects and charge transfer in lanthanum cobaltite

Abstract

The specific conductivity logσT and thermal electromotive force coefficient QT of perovskite-like lanthanum cobaltite were measured over the temperature range 1173 K ≤ T ≤ 1323 K depending on the partial pressure of oxygen (10−8 atm ≤ pO2 ≤ 1 atm). The pO2-T-δ phase diagram of solid LaCoO3-δ studied earlier was used to recalculate the electric property data into the log σT-δ and QT-δ dependences. The isoconcentration temperature dependences of specific conductivity (logσ)δ-1/T and Seebeck coefficient Qδ-1/T for LaCoO3-δ were analyzed. The conclusion was drawn that charge transfer was activation in character and had a low activation energy. This was evidence that small-radius polarons (CoCo• and CoCo′) were responsible for charge transfer in perovskite-like lanthanum cobaltite. The calculated equilibrium constants for the formation of electronic defects and functional dependences of defect concentration [CoCo•]T = f1(δ) and [CoCo′]T = f2(δ) were used to analyze polaron transfer parameters in LaCoO3-δ.