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dc.contributor.author劉昱廷en_US
dc.contributor.authorLiu, Yu-Tingen_US
dc.contributor.author林俊源en_US
dc.date.accessioned2014-12-12T01:41:09Z-
dc.date.available2014-12-12T01:41:09Z-
dc.date.issued2009en_US
dc.identifier.urihttp://140.113.39.130/cdrfb3/record/nctu/#GT079727515en_US
dc.identifier.urihttp://hdl.handle.net/11536/45266-
dc.description.abstract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<y≦0.5)。我們的結論是Mn K-edge的研究無法回答這個問題。在變溫下La1-xCaxMnO3 (x=0.6、0.8)的O K-edge光譜與Mn K-edge光譜之pre-edge發現了與La0.7Ca0.3MnO3光譜相反的變化,原因是電荷有序也就是相干極化子(Correlated Polaron)使得電荷載子(charge carrier)侷域(localize)在Mn+3晶格點上,為了降低其能量而產生了Jahn-Teller distortion效應所造成的結果。由La1-xCaxMnO3 (x=0.6、0.8)與其它同系列樣品(x= 0、0.3、1)之Mn L-edge和Mn K-edge X光吸收光譜發現,在室溫時(T = 300K) La1-xCaxMnO3 (x=0.6、0.8)的錳離子為平均價數,隨著溫度降至低溫(T = 18K),Mn L-edge和Mn K-edge光譜幾乎無任何變化。   另一部份,我們使用同步輻射中心X光源測量一系列有關鉻的標準樣品之X光吸收光譜,分析其氧化價數對Cr K-edge吸收邊緣能量位置的變化,完成鉻化合物價數圖,亦用此圖來判斷Cr3(PO4)2、Cr2S3、CdCr2S4與CuCrO4中Cr的價數,並以L-edge加以佐證。實驗結果為:一. Cr2S3、CdCr2S4是Cr+2,CdCr2S4在光譜中呈現接近單一2+價數,然無價數分離之現象發生。二. Cr3(PO4)2是Cr+2,Cr3(PO4)2與CrF2在Cr L-edge光譜中極為相似,已知CrF2是高自旋態(high spin state),推論Cr3(PO4)2的自旋組態為相同的高自旋態(high spin state),並以磁性量測加以佐證。三. CuCrO4是Cr+6,可以輔助說明其Cu存在價數分離之現象。zh_TW
dc.description.abstractIn 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.en_US
dc.language.isozh_TWen_US
dc.subject鑭鈣錳氧zh_TW
dc.subject電荷有序zh_TW
dc.subject離子價數zh_TW
dc.subject相干極化子zh_TW
dc.subject吸收光譜zh_TW
dc.subjectLa1-xCaxMnO3en_US
dc.subjectcharge orderingen_US
dc.subjectionic valenceen_US
dc.subjectcorrelated polaronen_US
dc.subjectXANESen_US
dc.title過渡金屬化合物離子價數與電荷有序之吸收光譜研究zh_TW
dc.titleInvestigation on the charge ordering and ionic valence of transition metal compounds by the XANES spectroscopyen_US
dc.typeThesisen_US
dc.contributor.department物理研究所zh_TW
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