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ChemSusChem ; 10(14): 2978-2989, 2017 07 21.
Artigo em Inglês | MEDLINE | ID: mdl-28594114


The perovskite series Sr2 CoNb1-x Tix O6-δ (0≤x≤1) was investigated in the full compositional range to assess its potential as cathode material for solid oxide fuel cell (SOFC). The variation of transport properties and thus, the area specific resistances (ASR) are explained by a detailed investigation of the defect chemistry. Increasing the titanium content from x=0-1 produces both oxidation of Co3+ to Co4+ (from 0 up to 40 %) and oxygen vacancies (from 6.0 to 5.7 oxygen atom/formula unit), although each charge compensation mechanism predominates in different compositional ranges. Neutron diffraction reveals that samples with high Ti-contents lose a significant amount of oxygen upon heating above 600 K. Oxygen is partially recovered upon cooling as the oxygen release and uptake show noticeably different kinetics. The complex defect chemistry of these compounds, together with the compositional changes upon heating/cooling cycles and atmospheres, produce a complicated behavior of electrical conductivity. Cathodes containing Sr2 CoTiO6-δ display low ASR values, 0,13â€…Ω cm2 at 973 K, comparable to those of the best compounds reported so far, being a very promising cathode material for SOFC.

Condutividade Elétrica , Fontes de Energia Elétrica , Óxidos/química , Eletrodos , Oxigênio/química , Pressão , Temperatura
Dalton Trans ; 44(8): 3801-10, 2015 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-25609145


We report the rich magnetic behaviour of Sr2CoNb1-xTixO6 (0 ≤ x ≤ 0.5) oxides as a result of their complex microstructure. Although these oxides show an average simple-cubic perovskite structure, they present a flexible microstructure due to short-range ordering between Co/Ti and Nb cations in the perovskite B-sites. The microstructure consists of double-cubic perovskite domains grown in a simple-cubic perovskite matrix. The size and number of the double-cubic perovskite domains decrease as the Ti content increases. As a result of aliovalent substitution of Nb(5+) by Ti(4+) in the parent Sr2CoNbO6 mixed-valence Co(3+)/Co(4+) oxides are obtained. A spin glass-like state has been observed at low temperatures for all the series, with freezing temperatures increasing with the Ti-content in the range 22 to 33 K. Furthermore, the x = 0.3 and x = 0.5 samples show non-interacting superparamagnetic particle-like dynamics associated with relatively high amounts of Co(4+), with "blocking temperatures" of 13 and ∼16 K, respectively. The complex magnetic behaviour of the title oxides seems to be connected with the clustering of magnetic Co(3+) and the distribution of Co(4+) as a result of the microstructure.