Correlating structure and oxygen non-stoichiometry with transport behaviour of mixed ionic-electronic conducting perovskite-related oxides

Mixed ionic-electronic conductors (MIECs) with perovskite-related structures hold potential for application as oxygen transport membranes (OTMs) and electrodes of solid oxide fuel cells (SOFCs). This thesis involves a number of studies on mixed ionic-electronic conducting perovskite and perovskite-related oxides. The main emphasis is on correlating crystal structure and oxygen non-stoichiometry with the oxygen transport properties exhibited by the oxides.
Ruddlesden-Popper (RP) type oxides are the subject of investigation in chapters 2 and 3. Chapter 2 investigates the influence of decomposition of Pr2NiO4+δ, at 750 °C, on the oxygen permeation flux, oxygen diffusion and surface exchange kinetics. Chapter 3 investigates the structure, electrical conductivity and oxygen transport properties of La2NiO4+δ, Nd2NiO4+δ, La3Ni2O7-δ, La4Ni3O10-δ, Pr4Ni3O10-δ and Nd4Ni3O10-δ. The oxygen migration mechanism of the 2nd and 3rd order RP phases is briefly discussed. In chapters 4 to 6, the focus is changed to perovskite oxides. Chapter 4 investigates the influence of the type of alkaline-earth-metal dopant on crystal structure, electrical conductivity and oxygen transport of perovskite-type oxides La0.6A0.4FeO3-δ (A = Ca, Sr and Ba). Chapter 5 further puts emphasis on perovskite-type oxides La1-xCaxFeO3-δ (x = 0.05, 0.10, 0.15, 0.20, 0.30 and 0.40). In addition to thermal evolution of crystal structure, oxygen nonstoichiometry, electronic and ionic conductivity, and oxygen diffusivity of the materials, the correlation between the migration barrier of oxygen in La1-xCaxFeO3-δ with dopant concentration and formation enthalpy of oxygen vacancies is explored. Chapter 6 investigates the structure and oxygen transport properties of perovskite-type CaMnO3-δ after partial substitution of the manganese ions with iron and/or titanium.