resumo
In order to study the behavior of perovskite-type phases containing similar fractions of transition metal cations and ions with stable oxidation state in the B sublattice, the defect formation processes in mixed-conducting Lac(0.90)Sr(0.10)Al(0.45)Fe(0.40)Mg(0.15)O(3-delta) were analyzed using the measurements of total conductivity in the oxygen partial pressure range from 10(-20) to 0.5 atm, at 1073-1223 K. The results, in combination with Mossbauer spectroscopy data and ion transference numbers determined by the faradaic efficiency technique in air, show that increasing p(O-2) leads to decreasing oxygen ionic conductivity, whilst no essential delocalization of the electronic charge carriers is observed. The variations of partial ionic and p- and n-type electronic conductivities can be adequately described by equilibrium processes of oxygen intercalation and iron disproportionation with the thermodynamic functions independent of defect concentrations. The hole mobility is also concentration-independent and has an activation energy of 37 +/- KJ/mol, suggesting that the p-type electronic transport occurs via a small-polaron mechanism within the whole p(O-2) range studied. The values of hole concentration derived from the conductivity data are in excellent agreement with the Mossbauer spectroscopy results. (c) 2005 Elsevier B.V. All rights reserved.
palavras-chave
PEROVSKITE-TYPE OXIDES; ELECTRONIC CONDUCTIVITY; OXYGEN NONSTOICHIOMETRY; MOSSBAUER-SPECTROSCOPY; SEEBECK COEFFICIENT; VACANCIES
categoria
Chemistry; Materials Science; Metallurgy & Metallurgical Engineering
autores
Tsipis, EV; Kharton, VV; Waerenborgh, JC; Rojas, DP; Naumovich, EN; Frade, JR
nossos autores
Jorge Ribeiro Frade
Professor(a) Jubilado(a)