Phase equilibrium and electrical conductivity of SrCo0:8Fe0:2O3
d

N. GRUNBAUM; L.V. MOGNI; F. PRADO; A. CANEIRO

JOURNAL OF SOLID STATE CHEMISTRY

ACADEMIC PRESS INC ELSEVIER SCIENCE

Lugar: Amsterdam; Año: 2004 vol. 177 p. 2350 - 2357

0022-4596

The phase diagram of the SrCo0:8Fe0:2O3d compound has been determined at high temperatures (823pTp1223 K) and in the oxygen partial pressure range (105ppO2p1 atm) by thermogravimetricmeasurements of the equilibrium pO2, high temperatureX-ray diffraction and electrical conductivity measurements. The cubic perovskite phase SrCo0:8Fe0:2O3d is stable in a broad range of oxygen content, while the orthorhombic brownmillerite phase SrCo0:8Fe0:2O2:5 stabilizes within a small range around 3d=2.5 attemperatures below 1073 K. Equilibrium pO2 measurements under isothermal conditions show chemical hysteresis at the perovskite to brownmillerite transition. The hysteresis loop decreases its amplitude in pO2 with decreasing temperature. This behavior is discussed considering the evolution from coherent intergrowth interfaces with elastic strain energy to incoherent interfaces without elasticstrain energy as T decreases. The thermodynamic quantities hoxideO2 and soxide O2 for the perovskite phase decrease when increasingthe oxygen defects concentration. The electrical conductivity (s) of the cubic phase exhibits a thermally activated behavior at high temperature. The variation of s with the oxygen content is non-linear and the activation energy varies from 0.4 to 0.28 eV as the oxygen content increases from 2.4 to 2.6. These results are interpreted in the frame of the small polaron model.