X-ray Absorption Spectroscopic Study on Valence State and Local Atomic Structure of Transition Metal Oxides Doped in MgH2

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• 作者：Nobuko Hanada ; Takayuki Ichikawa ; Shigehito Isobe ; Tessui Nakagawa ; Kazuhiko Tokoyoda ; Tetsuo Honma ; Hironobu Fujii ; Yoshitsugu Kojima
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：July 30, 2009
• 年：2009
• 卷：113
• 期：30
• 页码：13450-13455
• 全文大小：187K
• 年卷期：v.113,no.30(July 30, 2009)
• ISSN：1932-7455

文摘

A valence state and a local structure of transition metals (Nb, V, and Ti) in MgH₂ doped with metal oxides (Nb₂O₅, V₂O₅, and TiO₂^nano) by ball milling were examined by X-ray absorption spectroscopy (XAS). The main edge regions of the Nb, V, and Ti K-edges in the X-ray absorption near edge structure (XANES) profiles are located between 0 and +5 in the oxidation states. Since these spectra coincide with those of NbO, VO, and Ti₂O₃, respectively, the additives are reduced by MgH₂ to the metal oxides, which have lower oxidation states than those of the starting materials. Furthermore, in order to examine the local structures around the transition metal atoms, the extended X-ray absorption fine structure (EXAFS) spectra were analyzed. In the Fourier transformation curves of the EXAFS spectra, all samples doped with the metal oxides show two peaks corresponding to metal−oxygen and metal−metal bonds, being the same as the references of NbO, VO, and Ti₂O₃. The local structure formed after ball milling or dehydrogenation is close to that of each of the reduced metal oxides (NbO, VO, and Ti₂O₃) but in a more disarrangement state.