Seebeck coefficient and electrical conductivity of BSCF (Ba_0.5Sr_0.5Co_xFe_1 ?#xa0;xO_{3 ?#xa0;¦Ä}, 0 ?#xa0;x ?#xa0;0.8) as a function of temperature and partial oxygen press

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• 作者：Jae-Il Jung ; Scott T. Misture ; Doreen D. Edwards ; ^{dedwards@alfred.edu}
• 关键词：BSCF ; Barium strontium cobalt iron oxide ; Perovskite ; Solid oxide fuel cell ; Cathode ; Mixed ionic-electronic conductor ; Defect chemistry ; Seebeck coefficient ; Jonker plot
• 刊名：Solid State Ionics
• 出版年：2012
• 出版时间：5 January, 2012
• 年：2012
• 卷：206
• 期：Complete
• 页码：50-56
• 全文大小：785 K

文摘

The electrical conductivity and Seebeck coefficient of sintered BSCF ceramics (Ba_0.5Sr_0.5Co_xFe_1 ?#xA0;xO_{3 ?#xA0;¦Ä}, 0 ?#xA0;x ?#xA0;0.8) were simultaneously measured as a function of pO₂ (10^?#xA0;5 ?#xA0;pO₂ ?#xA0;1 atm) at 500 ¡ãC, 700 ¡ãC and 900 ¡ãC. All samples exhibited a positive Seebeck coefficient over the range of pO₂ and temperature examined, which indicates the predominance of p-type conduction. In all cases, conductivity increased with increasing pO₂, ranging from a minimum of ~ 0.6 S/cm (x = 0, pO₂ = 10^?#xA0;5 atm, T = 900 ¡ãC) to a maximum of ~ 36 S/cm (x = 0.8, pO₂ = 1 atm, and T = 900 ¡ãC). At low temperatures and high pO₂, conductivity was approximately proportional to pO₂^1/4, which was attributed to the reduction of B-site cations from their tetravalent to trivalent state. At low pO₂ and high temperature, the conductivity exhibited positive deviations from the pO₂^1/4 dependence. At 500 ¡ãC and x ?#xA0;0.6, the Seebeck coefficient (Q) decreased linearly with increasing log pO₂. At 700 and 900 ¡ãC, Q vs. log pO₂ curves exhibited maxima at 10^?#xA0;3 < pO₂ < 10^?#xA0;1 atm, and the maxima shifted to higher pO₂ as x increased. A simple p-type polaron hopping model, assuming negligible contribution from n-type or ionic carriers, was used to extract the carrier concentration of the x = 0.8 sample from the measured thermopower data. The calculated hole mobility for the x = 0.8 sample was less than 0.1 cm²/V-s, confirming a p-type polaron-hopping model. This analysis, as well as analysis of Jonker plots, suggested that hole mobility decreased with decreasing pO₂.