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The Crystal structure of $$delta$$-Al(OH)$$_{3}$$; Neutron diffraction measurements and ab initio calculations

$$delta$$-Al(OH)$$_{3}$$の結晶構造; 中性子回折測定と第一原理計算

松井 正典*; 小松 一生*; 池田 恵美*; 佐野 亜沙美  ; 後藤 弘匡*; 八木 健彦*

Matsui, Masanori*; Komatsu, Kazuki*; Ikeda, Emi*; Sano, Asami; Goto, Hirotada*; Yagi, Takehiko*

中性子回折実験により、$$delta$$-Al(OD)$$_{3}$$の結晶構造は以前X線回折実験に基づいて報告された${it Pnma}$ではなく${it P}$2$$_{1}$$2$$_{1}$$2$$_{1}$$であることが明らかになった。AlとOの位置はX線回折実験により求めた値を使用し、水素位置は第一原理計算により求めた値を用いて解析を行ったところ、第一原理計算の結果は中性子回折実験の結果とよく一致するものであった。また67GPa付近で${it P}$2$$_{1}$$2$$_{1}$$2$$_{1}$$構造から${it Pnma}$構造へと相転移し、水素が二つの酸素間の中心に位置する対称化が起きることが第一原理計算から示唆された。

Neutron powder diffraction analyses of $$delta$$-Al(OD)$$_{3}$$ revealed that the crystals are orthorhombic with space group ${it P}$2$$_{1}$$2$$_{1}$$2$$_{1}$$, but not ${it Pnma}$ as reported previously by X-ray diffraction data. The initial lattice parameters and the atomic positions of both Al and O were taken from previous X-ray structural analyses for the ${it Pnma}$ structure, while the H atom positions were determined using ab initio calculations. The $$delta$$-Al(OH)$$_{3}$$ structure possesses one relatively long and two short O-H...O hydrogen bonds. Ab initio calculations are also used to find that $$delta$$-Al(OH)$$_{3}$$ with space group ${it P}$2$$_{1}$$2$$_{1}$$2$$_{1}$$ transforms to another high pressure polymorph with space group ${it Pnma}$ at around 67 GPa, and that the two short hydrogen bonds in $$delta$$-Al(OH)$$_{3}$$ become both symmetric through the transformation, in which the protons are located at the midpoints of the O...O hydrogen bonds.

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パーセンタイル:40.6

分野:Geochemistry & Geophysics

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