Phase stability and structural distortions of nanostructured titanium-cobaltite

NAPOLITANO, FEDERICO; LAMAS, DIEGO; BAQUÉ, LAURA; SOLDATI, ANALIA L.; SERQUIS, ADRIANA C.

Campinas

Encuentro; RAU23_Reunión Anual de Usuarios de LNLS; 2013

Laboratorio Nacional de Luz Sincrotrón

In this work we report the synthesis (by a low-temperature chemical route) and thestructural characterization of lanthanum strontium titanates based oxides. Thesematerials with perovskite-type crystal structure are good candidates for symmet-rical solid-oxide fuel cell electrodes. The room temperature crystal structure ofLa0:4Sr0:6Ti1¡yCoyO3¡± (0:0 · y · 0:5) oxides, not previously reported beforefor y 6= 0, was studied by XPD. Structural parameters obtained by Rietveld re¯ne-ments of synchrotron X-ray powder di®raction data allowed to identify that A-sitevacancies creation is the dominant charge compensation mechanism at low cobaltcontent level but, as Co concentration is increased from y = 0:0 to 0.3 there is atransfer to another mechanism (e.g. Co oxidation state changes). For y ¸ 0:3 theSr content (and consequently A-site vacancies) stabilizes. A correlation was foundbetween A-site vacancy concentration and lattice parameter evolution as a functionof Co content. A rhombohedric to cubic (R¹3c at room temperature to Pm¹3m at750±C) phase transition was established for La0:4Sr0:6Ti0:7Co0:3O3+± compositionfrom high temperature measurements. Meanwhile, no further structural changeswas observed as the atmosphere was changed from synthetic air to 5%H2=95%Heat 750±C, simulating cathode and anode working condition, respectively. Besides,no signi¯cant di®erences on lattice parameters were found comparing samples syn-thesized at 850 and 1100 ±C. The same dependence in perovskite A-site vacancyconcentration and structural distortion level were observed for both sample se-ries, but the charge compensation mechanism shift was favored and the structuraldistortion level was increased in the series of higher synthesis temperature.