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Evaluation of electronic state of Cs-adsorbed clay minerals by NEXAFS analysis using DFT calculations

DFTを用いたNEXAFS分析によるCs吸着粘土鉱物の電子状態評価

鈴木 知史; 矢板 毅; 鈴木 伸一; Pacold, J.*; Altman, A. B.*; Minasian, S. G.*; Tyliszczak, T.*; Shuh, D. K.*; 吉田 啓之; 逢坂 正彦

Suzuki, Chikashi; Yaita, Tsuyoshi; Suzuki, Shinichi; Pacold, J.*; Altman, A. B.*; Minasian, S. G.*; Tyliszczak, T.*; Shuk, D. K.*; Yoshida, Hiroyuki; Osaka, Masahiko

密度汎関数法(DFT: density-functional theory)を用いて、Cs M$$_{4,5}$$ X線吸収端近傍微細構造(NEXAFS: near-edge X-ray absorption fine structure)スペクトルを解析する手法を確立し、粘土鉱物中のCsの電子状態を評価した。各種のCsハロゲン化物のDFTによる解析を行うことにより、内殻空孔強度を組み込みその値を最適化して、NEXAFSスペクトルの再現に成功した。本DFTによる解析手法を用いて、粘土鉱物のCs M$$_{4,5}$$ NEXAFSスペクトルを解析したところ、主要な遷移およびテール構造を含めて、実験によるNEXAFSスペクトルを良好に再現することができた。本手法を用いて、電荷密度や電子状態の解析を行い、NEXAFSスペクトルに現れる構造が結合状態およびCs原子の周りの局所環境を反映する可能性が高いこと、粘土鉱物中においてCsと最近接原子との相互作用が最も大きいこと等を示した。

A combined method of NEXAFS measurement and DFT-calculation was employed for Cs evaluation in clay minerals. The Cs M$$_{4,5}$$ NEXAFS spectra of Cs halides were analyzed using the DFT-calculations, and were well reproduced by incorporating the core-hole strength. The Cs M$$_{4,5}$$ NEXAFS spectrum of clay minerals was well-reproduced by the DFT-calculations including the major transitions and tail structures with the established method. The further evaluation of this spectrum by charge density suggests that these major transitions and the tail structures likely reflect bonding states and local environments around the Cs atoms. Comparison of electronic states of Cs in the clay mineral with those in the Cs halides by DFT-calculations has shown that the interaction between Cs and the nearest-neighbor atom is largest in the clay mineral, because the energy level of Cs-5s and 5p is closer to that of O-2s and 2p than the s and p orbitals of other alkali metal and alkali earth metal elements.

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パーセンタイル:100

分野:Chemistry, Multidisciplinary

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