Thermodynamic Quantities and Defect Chemical Properties of La0.8Sr0.2FeO3-δ

In this work, the defect structure analysis of La0.8Sr0.2FeO3-delta, (LSF82) was presented. Thermogravimetric measurements were performed to determine change in oxygen nonstoichiometry (Delta delta) with oxygen partial pressure (PO2) in 10(-19)<=(P-O2/atm) <= 0.21 and 750 <=(T/degrees C)<= 900 range. LSF82 showed a clear electronic stoichiometric point around delta approximate to 0.1. The negative sign of partial molar enthalpy (Delta(H) over bar (0)) and entropy (Delta(S) over bar (0)) indicated that the incorporation of oxygen was an exothermic process and showed that the experimentally observed variations in Delta(H) over bar (0) and Delta(S) over bar (0) with delta fitted well with the statistical thermodynamic analysis. The defect diagram analysis showed that in n-type regime Fe-Fe(/) concentration varied with (P-O2)(-1/4) whereas in p-type regime Fe center dot(Fe) concentration varied with (PO2)(+1/4). The electrical conductivity relaxation (ECR) experiments were performed to extract partial ionic conductivity and oxygen self diffusivity. The oxygen self-diffusivity (D-o) increased from 1.20 x 10(-8)cm(2).s(-1) at 800 degrees C to 3.54 x 10(-8 )cm(2).s(-1) at 900 degrees C with an activation energy of 1.17 +/- 0.23 eV. Dilatometry was performed for expansion measurements as function of P-O2 and temperature. The chemical expansion model based on the relative change in mean ionic radius vs. delta showed that Fe3+ existed as a mixture of high-spin and low-spin states and made a transition from low-spin to high-spin state with increasing delta. (C) 2018 The Electrochemical Society.