過渡金屬化合物離子價數與電荷有序之吸收光譜研究

Investigation on the charge ordering and ionic valence of transition metal compounds by the XANES spectroscopy

劉昱廷(Yu-Ting Liu)

指導教授 ： 林俊源

國立交通大學/理學院/物理研究所/碩士(2010年)

https://doi.org/10.6842/NCTU.2010.00913

摘要

本論文利用同步輻射中心X光源進行隨著溫度改變之O K-edge、Mn L-edge和Mn K-edge X光近緣吸收結構(XANES)實驗，探討La1-xCaxMnO3 (x=0.6、0.8)塊材在電荷有序(charge ordering)中錳離子是否會分成Mn+3與Mn+4交替排列，或只是分成較少差異的Mn+(3+y)與Mn+(4-y)(0

關鍵字

鑭鈣錳氧 ； 電荷有序 ； 離子價數 ； 相干極化子 ； 吸收光譜

並列摘要

In this thesis, x-ray absorption near edge spectroscopy (XANES) experiments were conducted in a range of temperatures upon La1-xCaxMnO3 (x=0.6, 0.8) using synchrotron radiation from the National Synchrotron Radiation Research Center (NSRRC). The O K-edge, Mn L-edge and Mn K-edge absorption spectra at different temperatures were obtained. Further analysis probes the nature of the charge ordering of Mn ions in La1-xCaxMnO3 (x=0.6、0.8) samples. The Mn K-edge spectra were meant to determine the degree of charge disproportion in charge ordered samples. As temperature changed, opposite trends developed in the O K-edge spectra and the Mn K-edge pre-edge spectra of charge ordered La1-xCaxMnO3 (x=0.6, 0.8) and La0.7Ca0.3MnO3 without charge ordering. They were results of the charge ordering. The correlated polaron localizes charge carriers in Mn+3 lattice points and hence results in Jahn-Teller distortion effect.

In another series of XANES experiments, the x-ray absorption spectra of standard samples of chromium were obtained. The correlation between the oxidation state and the Cr K-edge absorption edge energy was investigated. A chromium valence state vs. K-edge energy chart was obtained, from which the valence states of Cr in Cr3(PO4)2, Cr2S3, CdCr2S4 and CuCrO4 were determined and verified with L-edge absorption spectrum. The valence of Cr was found to be +6 in CuCrO4, and+2 in Cr3(PO4)2, Cr2S3, CdCr2S4. Furthermore, Cr3(PO4)2 is found to be in high spin state, as its L-edge spectrum highly resembles that of CrF2. This result was testified by the magnetic measurements. Lastly, the valence of Cr was found to be +6 in CuCrO4, which aids the explanation of the charge disproportion of Cu in this compound.

並列關鍵字

La1-xCaxMnO3 ； charge ordering ； ionic valence ； correlated polaron ； XANES

參考文獻

[4] 李佩茹，碩士論文，” 過渡金屬氧化物之近緣吸收光譜研究”，交通大學，(2008)。

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