The Crystal structure of -Al(OH); Neutron diffraction measurements and ab initio calculations

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

Neutron powder diffraction analyses of -Al(OD) revealed that the crystals are orthorhombic with space group 222, but not 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 structure, while the H atom positions were determined using ab initio calculations. The -Al(OH) structure possesses one relatively long and two short O-H...O hydrogen bonds. Ab initio calculations are also used to find that -Al(OH) with space group 222 transforms to another high pressure polymorph with space group at around 67 GPa, and that the two short hydrogen bonds in -Al(OH) become both symmetric through the transformation, in which the protons are located at the midpoints of the O...O hydrogen bonds.