Defect Structure and Electrical Conductivity of Ruddlesde-Popper Phases Sr3FeMO6+ (M = Co, Ni).

L. MOGNI; F. PRADO; A. CANEIRO

CHEMISTRY OF MATERIALS

American Chemical Society

Año: 2006 vol. 18 p. 4163 - 4170

0897-4756

 In this work we report a systematic study of the oxygen non-stoichiometry, high temperature thermodynamic and transport properties of the perovskite related mixed conductors Sr3FeMO6+d (M = Co, Ni). The variation of the oxygen content (6+d) with T and equilibrium oxygen partial pressure (pO2) was obtained by thermogravimetry within the range: 10-5 < pO2 < 1 atm.; 400 £ T £ 1000 °C. From the experimental values of the oxygen chemical potential ( ), the partial molar enthalpy ( ) and the partial molar entropy ( ) were determined for the composition range 6.00 < “6+d” < 6.55. A simple defect model based on the mass action law assuming oxygen vacancies formation and involving different fractions of localized and delocalized charge carriers in iron sites and metal transition M3d-O2p band respectively was used to reproduce the thermodynamic data. Electrical resistivity measurements as a function of pO2 at constant temperature were obtained within the interval 650 £ T £ 1000 ºC for Sr3FeCoO6+d and Sr3FeNiO6+d compounds. The activation energy values for the electrical transport process at constant oxygen content values were obtained from the combination of electrical conductivity and thermogravimetry data. The electrical conductivity data are understood into the frame of large polaron behavior in agreement with the thermodynamic data.