层状钴氧化物Bi_(2-x)Ag_xSr_2Co_2O_(8-δ)的高温热电性能及XPS研究(英文)

High-temperature Thermoelectric Properties and X-ray Photoemission Spectra of Layered Co-based Oxides Bi_(2-x)Ag_xSr_2Co_2O_(8-δ)

采用固相反应法制备了组成为Bi_(2-x)Ag_xSr_2Co2O_(8-δ)(x=0.0,0.4,0.8,略写为BAC-222)的层状钴氧化物陶瓷。利用X-射线光电子能谱考察该类化合物的电子结构,结果表明钴离子以Co3+和Co4+混合价态形式存在,nCo4+/nCo3+的比例随着Ag掺杂的量增加而增加。O1s光电子谱显示在所有样品中均存在点阵氧和吸附氧。热电性能测试结果显示,随着Ag掺杂量的增加,电导率显著增加而Seebeck系数几乎保持不变,Ag的引入极大的影响了BAC-222的电子输运性质,其功率因子在1123K时达到了1.23×10-4W·m-1·K-2,是一种具有很好应用前景的热电材料。

Layered Co-based ceramics with a nominal composition of Bi2-xAgxSr2Co2O8-δ（x=0.0, 0.4, 0.8, denoted by BAC-222） were prepared using conventional solid state reaction method. X-ray photoemission spectroscopy（XPS） was used to investigate their electronic structures. The cobalt ions are existed in mixed states of Co^3＋ and Co^4＋. It is found that the nCo^4＋/nCo^3＋ ratio increases with the Ag doping content. The O1s photoemission spectra show that there are lattice oxygen and chemical absorbed oxygen in all the samples. Meanwhile, the conductivity and Seebeck coefficient of Bi2-xAgxSr2Co2O8-δ were studied. The substitution of Bi^3＋ by Ag^＋ results in dramatically increase of the electrical conductivity while the Seebeck coefficient is kept almost unchanged. This abnormal phenomenon means that Ag＋ ions play an important role in the electrical transport property of BAC-222. The power factor of Bi1.6Ag0.4Sr2Co2O8-δ reaches 1.23×10^-4 W·m^-1·K^-2 at 1 123 K, which suggests that Bi2-xAgxSr2Co2O8-δ are good potential oxides for thermoelectric application.