Oxygen nonstoichiometry, defect structure and electrical properties of LaFe 0.7Ni 0.3O 3 − δ

Abstract

Oxygen nonstoichiometry ( δ), total conductivity ( σ) and thermoelectric power ( S) of the LaFe 0.7Ni 0.3O 3 − 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(O 2) = 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 LaFe 0.7Ni 0.3O 3 − δ has been explained by the higher mobility values of electron holes than those of electrons in the whole range of thermodynamic parameters studied.