稀土元素摻雜對Ca3Co4O9 熱電材料電子結構之影響

Effect of rare-earth-doping on the electronic structure of Ca3Co4O9 thermoelectric material studied

高郁智(Yu-Chih Kao)

指導教授 ： 張經霖

淡江大學/理學院/物理學系碩士班/碩士(2010年)

https://doi.org/10.6846/TKU.2010.00843

摘要

本論文是利用X光吸收光譜(XANES)對以稀土元素部分取代Ca之Ca3Co4O9樣品進行有系統的研究。摻入的元素包括Pr、Dy、Ho、Er、Yb與Lu，其摻雜量均為0.1。摻雜之稀土元素的價數均比Ca大，Ca被稀土取代後會有多餘的價電子出現，而由Co K-edge 和Ca L3-edge XANES發現其光譜吸收強度在稀土元素摻雜之後都變小，即表示Co 4p與Ca 3d空軌域均減少，有電子轉移到Co 4p與Ca 3d空軌域。稀土元素的離子半徑隨著原子序增加而減小，而Co K-edge 和Ca L3-edge光譜吸收強度變化與摻雜元素之離子半徑有一定的關聯性，隨著摻雜稀土元素之離子半徑減小而Co K-edge 和Ca L3-edge吸收強度漸漸增強。但是摻雜Yb及Lu的樣品可能因為Yb的價數較小，而Lu的離子半徑只比Yb小1 %，因此摻雜Yb及Lu的樣品受離子半徑效應的影響比較不明顯。Co L3-edge和O K-edge XANES則顯示其吸收強度的改變隨著各種不同稀土元素的摻雜而有不一樣的變化，其空軌域有增有減。

關鍵字

X光吸收光譜近邊結構 ； 熱電材料 ； Ca3Co4O9

並列摘要

We have performed x-ray absorption near edge structure (XANES) study on rare-earth-doped thermoelectric materials based on Ca3Co4O9. Samples are doped with various rare-earth elements, including Pr, Dy, Ho, Er, Yb and Lu, and the doping level is fixed at 0.1. Co K-edge and Ca L3-edge XANES become weaker in rare-earth doped samples, which indicates the unoccupied state of Ca 3d and Co 4p are decreased compared to the undoped sample. It also indicates that there may have some electrons transferred into Ca 3d and Co 4p states. The ionic radii of rare-earth element decreases with increasing atomic number. A correlation between the intensities of Co K-edge and Ca L3-edge XANES and the ionic radii of rare-earth elements were observed. We attribute this correlation to the effects of the higher valence and the various ionic radii of the doped elements.

並列關鍵字

XANES ； thermoelectric material ； Ca3Co4O9

參考文獻

Abhandlungen der Deutschen Akademie Wissenschaften zu Berlin,

[2] I. Terasaki et al., Phys. Rev. B 56, R12685 (1997).

[3] Ryoji Asahi et al., Phys. Rev. B 66, 155103 (2002).

[4] D. Pelloquin et al., Solid State Science, 6, 167-172 (2004).

[6] J. Sugiyama et al., Phys. Rev. B 68, 134423 (2003).