以吸收光譜研究量子物質Ba3V2S4O3、FeSe、K2Mn3(VO4)2(CO3)與Mn2BO4

Abstract

本實驗與德國Max Planck Institute中Zhiwei Hu等人合作，利用同步輻射光分別探討Ba3V2S4O3、FeSe、K2Mn3(VO4)2(CO3)與Mn2BO4四種樣品之價數和電子結構。 本論文中Ba3V2S4O3是以量測V L-edge之X光近緣吸收光譜(XANES)來探討釩離子對應在晶體結構為tetrahedral四配位和octahedral六配位之離子價數，再經由multiplet理論計算來加以推定。由結果得知，Ba3V2S4O3之釩離子價數為正三價時，其對應的配位數為六配位octahedral site，即V3+S6；釩離子價數為正五價時，其對應的配位數為四配位tetrahedral site，即V5+O3S。 本論文亦對K2Mn3(VO4)2(CO3)進行Mn L-edge之X光近緣吸收光譜(XANES)實驗並結合理論計算，探討Mn離子在K2Mn3(VO4)2(CO3)晶體結構中octahedral 與trigonal site之自旋態。而我們成功分析出在K2Mn3(VO4)2(CO3)樣品中，二價錳離子在octahedral 與trigonal site皆展現出S=5/2之高自旋態(HS)。 此外，本論文也對FeSe單晶在溫度為T=300 K、105 K、75 K與15 K進行一系列變溫Fe L-edge之X光近緣吸收光譜(XANES)實驗，並探討隨著溫度變化是否能觀察到由nematic order在FeSe上所造成的電子結構的異向性。雖然在Fe L-edge光譜上並無發現由nematic order所造成的電子結構的異向性，卻也因樣品品質相較其它文獻中之樣品品質好而量測到品質較高的Fe L-edge光譜，並成功應證了文獻中之理論計算結果。 最後，在Mn2BO4樣品上，本論文進行了Mn K、L-edge之X光近緣吸收光譜(XANES)實驗來探討錳離子在Mn2BO4中之價態。而Mn K-edge與L-edge光譜之結論皆指出，錳離子自是以1：1的Mn2+與Mn3+存在於Mn2BO4中。

In cooperation with Zhiwei Hu from Max Planck Institute, this thesis discusses the valence state and electronic structure in cases of Ba3V2S4O3, K2Mn3(VO4)2(CO3), Mn2BO4 and FeSe through the investigation by applying synchrotron radiation on the sample. In this thesis, Ba3V2S4O3 V L-edge is measured by using X-ray absorption near edge spectroscopy (XANES) in order to explore the vanadium valence state at both tetrahedral and octahedral sites. In addition, the measurement is also confirmed by multiplet theoretical calculations through simulating the experimental spectrum. The theoretical calculations suggest that vanadium ions are trivalent and pentavalent in the coordination of V3+S6 and V5+O3S respectively. In the K2Mn3(VO4)2(CO3) case, we measured Mn L-edge by using X-ray absorption near edge spectroscopy (XANES) to explore the spin state in octahedral and trigonal sites. Combined with theoretical calculation, we confirm that the divalent manganese exhibits the high spin state (S=5/2) in both octahedral and trigonal sites. In addition, in order to discuss whether the observation of the electronic structure anisotropy in FeSe caused by nematic order is possible or not under temperature variations, Fe L-edge is measured by using X-ray absorption near edge spectroscopy (XANES) at T=300 K, 105 K, 75 K and 15 K. Although the result shows no evidence of electronic structure anisotropy in Fe L-edge spectrum, the higher quality of FeSe used here than those in literatures makes a better Fe L-edge spectrum available, which leads to the successful verification of the theoretical calculations from literatures. Moreover, we measured Mn K, L-edge XANES spectra in Mn2BO4 to confirm the manganese valence state. The spectrum in both Mn K-edge and L-edge suggests that manganese ions in Mn2BO4 have shown the 1:1 ratios from Mn2+ and Mn3+ in Mn2BO4.