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

Oxygen nonstoichiometry (6), total conductivity (a) and thermoelectric power (S) of the LaFe0.7Ni0.3O3-delta 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 degrees C the absolute oxygen content (3 - delta) 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(delta)(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-delta has been explained by the higher mobility values of electron holes than those of electrons in the whole range of thermodynamic parameters studied. (C) 2011 Elsevier B.V. All rights reserved.