Oxygen nonstoichiometry, defect structure and electrical properties of LaFe0.7Ni0.3O3 − δ

Oxygen nonstoichiometry (δ), total conductivity (σ) and thermoelectric power (S) of the LaFe0.7Ni0.3O3 − δ sample have been studied as functions of temperature and oxygen partial pressure. Based on the results of the direct reduction of the sample in hydrogen flow at 1100 °C the absolute oxygen content (3 − δ) has been found to vary from 2.999 to 2.974 in the range of 1273–1373 K and 10− 3–0.21 atm. The point defect equilibrium models have been proposed and fitted to the set of experimental data in the form of log p(O2) = f(δ)T dependences. The values of standard thermodynamic quantities of defect formation reactions have been assessed. The joint analysis of oxygen nonstoichiometry, total conductivity and thermoelectric power has been performed using a small-polaron approach. The values of partial conductivity, partial thermopower and mobilities of electronic charge carriers have been calculated. The p-type semiconducting behavior of LaFe0.7Ni0.3O3 − δ has been explained by the higher mobility values of electron holes than those of electrons in the whole range of thermodynamic parameters studied.

Research Highlights
► We obtained the p(O2)-T dependences of δ, σ, and S for LaFe0.7Ni0.3O3–δ.
► The dependences were interpreted on the basis of point defect models.
► The standard thermodynamic properties of point defect reactions were calculated.
► The mobility values for electrons and holes were assessed.
► The p-type semiconducting behavior of LaFe0.7Ni0.3O3–δ was explained.