Gallium Arsenate Dihydrate under Pressure: Elastic Properties, Compression Mechanism, and Hydrogen Bonding

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• 作者：Elinor C. Spencer ; Victoria Soghomonian ; Nancy L. Ross
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：August 3, 2015
• 年：2015
• 卷：54
• 期：15
• 页码：7548-7554
• 全文大小：359K
• ISSN：1520-510X

文摘

Gallium arsenate dihydrate is a member of a class of isostructural compounds, with the general formula M³⁺AsO₄路2H₂O (M³⁺ = Fe, Al, In, or Ga), which are being considered as potential solid-state storage media for the sequestration of toxic arsenic cations. We report the first high-pressure structural analysis of a metal arsenate dihydrate, namely, GaAsO₄路2H₂O. This compound crystallizes in the orthorhombic space group Pbca with Z = 8. Accurate unit cell parameters as a function of pressure were obtained by high-pressure single-crystal X-ray diffraction, and a bulk modulus of 51.1(3) GPa for GaAsO₄路2H₂O was determined from a third-order Birch鈥揗urnaghan equation of state fit to the P鈥?i>V data. Assessment of the pressure dependencies of the unit cell lengths showed that the compressibility of the structure along the axial directions increases in the order of [010] < [100] < [001]. This order was found to correlate well with the proposed compression mechanism for GaAsO₄路2H₂O, which involves deformation of the internal channel void spaces of the polyhedral helices that lie parallel to the [010] direction, and increased distortion of the GaO₆ octahedra. The findings of the high-pressure diffraction experiment were further supported by the results from variable-pressure Raman analysis of GaAsO₄路2H₂O. Moreover, we propose a revised and more complex model for the hydrogen-bonding scheme in GaAsO₄路2H₂O, and on the basis of this revision, we reassigned the peaks in the OH stretching regions of previously published Raman spectra of this compound.