resumo
The substitution of manganese with nickel in LaSr2Mn2O7-delta, where the solubility limit corresponds to approximately 25% Mn sites, enhances the Ruddlesden-Popper phase stability at elevated temperatures and atmospheric oxygen pressure. The total conductivity of LaSr2Mn2-yNiyO7-delta (y = 0-0.4) decreases with nickel additions, whilst the average thermal expansion coefficients calculated from dilatometric data in the temperature range 300-1370K increase from (11.4-13.7)x K` at y = 0 up to (12.5-14.4) x 10(-6) K-1 at y = 0.4. The conductivity and Seebeck coefficient of LaSr2Mn1.6CNi0.4O7-delta, analyzed in the oxygen partial pressure range 10(-15)-0.3 atm at 600-1270 K, display that the electronic transport is n-type and occurs via a small polaron mechanism. Reductive decomposition is observed at the oxygen pressures close to Ni/NiO boundary, namely similar to 2.3 x 10(-11) atm at 1223 K. Within the phase stability domain, the electronic transport properties are essentially p(O-2)-independent. The steady-state oxygen permeability of dense LaSr2Mn1.6Ni0.4O7-delta membranes is higher than that of(La,Sr)MnO3-delta, but lower if compared to perovskite-like (Sr,Ce)MnO3-delta. Porous LaSr2Mn1.6Ni0.4O7-delta cathodes in contact with apatite-type La10Si5AlO26.5 solid electrolyte exhibit, however, a relatively poor electrochemical performance, partly associated with strong cation interdiffusion between the materials. (C) 2008 Elsevier Inc. All rights reserved.
palavras-chave
MAGNETIC-PROPERTIES; O SYSTEM; ELECTROCHEMICAL-BEHAVIOR; THERMODYNAMIC PROPERTIES; OXYGEN NONSTOICHIOMETRY; PHASE-EQUILIBRIA; OXIDES; CONDUCTIVITY; MAGNETORESISTANCE; STABILITY
categoria
Chemistry
autores
Yaremchenko, AA; Bannikov, DO; Kovalevsky, AV; Cherepanov, VA; Kharton, VV
nossos autores
Aleksey Yaremchenko
Investigador Principal
Andrei Kavaleuski
Investigador principal
Vladislav Kharton
Investigador Principal Covidadoagradecimentos
This work was supported by the FCT, Portugal (Project PTDC/CTM/64357/2006), and by the Belgian Federal Science Policy foundation.