Defect Structure, Transport Properties, and Chemical Expansion in Ba0.95La0.05FeO3– δ

Abstract

This work systematically investigates the oxygen nonstoichiometry, defect structure and mass/charge transport properties of Ba0.95La0.05FeO3−δ (BLF). Thermogravimetric measurement and coulometric titration were performed to determine change in oxygen nonstoichiometry (δ) with oxygen partial pressure () in 10−17 ≤ (/atm) ≤ 0.21 and 850 ≤ (T/°C)≤900 range. The δ−−T plot showed “S-type” shape with a crossover plateau around δ ≈ 0.475. Defect modelling was used to explain the nonstoichiometry data and partial molar thermodynamic quantities for oxygen were determined. The DC 4-probe conductivity measurement was performed which showed a typical semiconductor-to-metal transition with temperature around the conductivity maxima at 450 °C. Electrical conductivity relaxation (ECR) measurement was performed to extract partial ionic conductivity, chemical diffusivity and surface exchange kinetics of oxygen ion by using Nernst-Einstein equation and Fick’s law. Isothermal chemical expansion was measured by dilatometry measurement in the range of 10−2 ≤ (/atm) ≤ 0.21 and 850 ≤ (T/°C) ≤ 950.