I.L. Ivanov

Oxygen nonstoichiometry, defect structure and related properties of LaNi0.6Fe0.4O3−δ

Experimental results on oxygen nonstoichiometry (δ), thermal and chemical expansion (ΔL/L0), total electrical conductivity (σ) and Seebeck coefficient (Q) as functions of the oxygen partial pressure (pO2) and temperature for LaNi0.6Fe0.4O3−δ are presented. The defect structure model of LaNi0.6Fe0.4O3−δ based on the localized nature of the electronic defects was proposed and successfully verified using the measured δ = f(pO2, T) dependences. On the basis of the model proposed the concentrations of the point defects were calculated as functions of the T and pO2. These concentrations were then employed in the model of chemical expansion and that of Seebeck coefficient. It was shown that both models coincide completely with the corresponding experimental data. The chemical expansion coefficients (βc) and mobilities of the charge carriers (electrons and holes) as functions of T and pO2 were calculated as a result.

In Situ and ex Situ Study of Cubic La0.5Ba0.5CoO3−δ to Double Perovskite LaBaCo2O6−δ Transition and Formation of Domain Textured Phases with Fast Oxygen Exchange Capability

The disordered La0.5Ba0.5CoO3-δ ↔ ordered LaBaCo2O6-δ transition was studied in detail using several complementary in situ (X-ray diffraction, thermogravimetry, and coulometric titration) and ex situ (transmission electron microscopy) techniques. This transition was found to proceed through the formation of complex domain textured intermediate products. They were shown to have strong affinity to oxygen and exhibit its fast absorption from ambient atmosphere (oxygen partial pressure ( pO2) 0.21 atm) at a temperature as low as 70 °C. The thermodynamic stability limits of the cubic and double perovskites were determined by coulometric titration. The stability diagram of the LaBaCo2O6-δ - La0.5Ba0.5CoO3-δ system was plotted as a result. Oxygen nonstoichiometry of the thermodynamically stable cubic perovskite La0.5Ba0.5CoO3-δ was measured as a function of pO2 in the temperature range between 1000 and 1100 °C using a coulometric titration technique.