Ga Substitution and Oxygen Diffusion Kinetics in Ca3Co4O9+未-Based Thermoelectric Oxides

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• 作者：Ruoming Tian ; Richard Donelson ; Chris D. Ling ; Peter E. R. Blanchard ; Tianshu Zhang ; Dewei Chu ; Thiam Teck Tan ; Sean Li
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：July 3, 2013
• 年：2013
• 卷：117
• 期：26
• 页码：13382-13387
• 全文大小：311K
• 年卷期：v.117,no.26(July 3, 2013)
• ISSN：1932-7455

文摘

The influence of Ga doping on the crystal structure and cobalt oxidation state of Ca₃Co₄O_9+未 was determined using synchrotron X-ray diffraction and X-ray absorption near-edge spectroscopy. The results show that Ga is preferentially located on the Co site in the rock-salt-type [Ca₂CoO₃] layer, up to a maximum occupancy of 2.2%, and that doping does not change the cobalt oxidation state of this material. We find that the doping-induced point defect scattering and modification of charge carrier concentration result in lower thermal conductivity and lower electrical resistivity, thereby improving the thermoelectric figure of merit in the Ga-doped Ca₃Co₄O_9+未 material. In addition, the influence of sample density and measuring atmosphere on their thermoelectric performance was found to be significant. It is believed that the interconnected pore structure in the low-density sample facilitates oxygen out-diffusion from the lattice, which leads to anomalous electrical resistivity behavior at elevated temperatures. We show that this behavior can be effectively suppressed by improving the sample density.