Improved Oxide Ion Conductivity in La0.8Sr0.2Ga0.8Mg0.2O3 by Doping Co

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• 作者：Tatsumi Ishihara ; Haruyoshi Furutani ; Miho Honda ; Takashi Yamada ; Takaaki Shibayama ; Taner Akbay ; Natsuko Sakai ; Harumi Yokokawa ; and Yusaku Takita
• 刊名：Chemistry of Materials
• 出版年：1999
• 出版时间：August 1999
• 年：1999
• 卷：11
• 期：8
• 页码：2081 - 2088
• 全文大小：119K
• 年卷期：v.11,no.8(August 1999)
• ISSN：1520-5002

文摘

The effects of doping Co for the Ga site on the oxide ion conductivity of La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ have been investigated in detail. It was found that doping Co is effective forenhancing the oxide ion conductivity. In particular, a significant increase in conductivity inthe low-temperature range was observed. The electrical conductivity was monotonicallyincreased; however, the transport number for the oxide ion decreased with an increasingamount of Co. Considering the transport number and ion transport number, an optimizedamount for the Co doping seems to exist at 8.5 mol % for Ga site. The theoretical electromotiveforces were exhibited on H₂-O₂ gas cell utilizing the optimized composition of La_0.8Sr_0.2Ga_0.8Mg_0.115Co_0.085O₃. The diffusion characteristics of the oxide ion in La_0.8Sr_0.2Ga_0.8Mg_0.115Co_0.085O₃ were also investigated by using the ¹⁸O tracer method. Since the diffusion coefficientmeasured by the ¹⁸O tracer method was similar to that estimated by the electricalconductivity, the conduction of La_0.8Sr_0.2Ga_0.8Mg_0.115Co_0.085O₃ is concluded to be almost ionic.On the other hand, an oxygen permeation measurement suggests that the oxide ionconductivity increased linearly with an increasing amount of Co. Therefore, specimens withCo content higher than 10 mol % can be considered as a superior mixed oxide ion and holeconductor. The UV-vis spectra suggests that the valence number of doped Co was changedfrom +3 to +2 with decreasing oxygen partial pressure; the origin of hole conduction canthus be assigned to the formation of Co³⁺. Since the amount of dopant in the Ga site wascompensated with Mg²⁺, the amount of oxygen deficiency was decreased by doping Co.Therefore, it is likely that the improved oxide ion conductivity observed by doping with Cois brought about by the enhanced mobility of oxide ion.