INVESTIGADORES
SOLDATI Analia Leticia
congresos y reuniones científicas
Título:
Phase stability and structural distortions of nanostructured iron-cobaltite mixed conductor
Autor/es:
BAQUÉ, LAURA; NAPOLITANO, FEDERICO; SOLDATI, ANALIA L.; CANEIRO, ALBERTO; SERQUIS, ADRIANA C.
Lugar:
Campinas
Reunión:
Congreso; RAU 22 - Reunión Anual Usuarios LNLS/CPEM; 2012
Institución organizadora:
Laboratorio Nacional de Luz Sincrotrón
Resumen:
Mixed conductors
oxides such as La1−xSrxCo1−yFeyO3−d are good candidates for
intermediate-temperature solid oxide fuel cells cathodes. Our previous studies
showed that the electrochemical performance is largely improved when using
cathodes prepared with nanosized La0.4Sr0.6Co0.8Fe0.2O3−d (LSCF) powders (i.e.
crystallite sizes 20-30 nm). However, an irreversibility increase in the
polarization resistance occurs after measurements under reductive atmospheres
in the 500-700 C
range, which seemed to be related to the presence of some unidentified lattice
distortions or an additional phase that could not be identified by conventional
laboratory X-ray powder diffraction (XPD). In this work, nanocrystalline LSCFO
powders were prepared by two different chemical methods. In-situ experiments
were carried out using the D10BXPD beamline at LNLS under different atmospheres
(pure He or synthetic air) between 20 and 600 C. In addition, some samples were prepared
ex-situ under Ar and O2 and studied by transmission electron microscope (TEM)
and laboratory XPD. The formation of phases with oxygen vacancy ordering was
observed for first time in the studied composition. The XPD data indicate that
only a portion of the sample is transformed while the rest keeps the original
phase. These results are in agreement with TEM observations that show the
coexistence of two phases in the same grain. All these changes can be reverted
with heat treatments under oxygen or air atmospheres.