Effect of La3+ doping on the perovskite-to-brownmillerite transformation in Sr1
xLaxCo0.8Fe0.2O3
d (0VxV0.4)

F. PRADO; N. GRUNBAUM; A. CANEIRO; A. MANTHIRAM

SOLID STATE IONICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2004 vol. 167 p. 147 - 154

0167-2738

The crystal chemistry of Sr1 xLaxCo0.8Fe0.2O3 d (0.0VxV0.4) has been investigated in the temperature range 20VTV900 jC andoxygen partial pressure range 10 5VpO2V1 atm, employing X-ray diffraction, electrical conductivity, and thermogravimetricmeasurements. The samples adopt the perovskite structure with pseudo-cubic or cubic symmetry at room temperature. With a decreasingoxidation state of (Fe,Co) from 3.5 to 3.27+, the oxygen content increases from 2.75 to 2.84 as the La content increases from 0 to 0.4.Electrical conductivity and thermogravimetric measurements indicate a complete transformation from the cubic perovskite to the orderedorthorhombic brownmillerite phase (P/B transition) for the x = 0 and 0.1 samples as the oxygen vacancy concentration d increases. For agiven temperature (T = 550 jC), the equilibrium pO2 at which the P/B transition occurs shifts to lower values as the La content increases.While phase analyses after annealing under vacuum or low pO2 conditions as well as high-temperature X-ray diffraction indicate theformation of the brownmillerite phases for xV0.3, the x = 0.4 sample is found to be stable without forming the brownmillerite phase underthe temperature and pO2 conditions investigated.