Compression and structure of brucite to 31 GPa from synchrotron X-ray diffraction and infrared spectroscopy studies
Maining Ma, Wei Liu, Zhiqiang Chen, Zhenxian Liu, and Baosheng Li
Abstract
Synchrotron X-ray powder diffraction and infrared (IR) spectroscopy studies on natural brucite were conducted up to 31 GPa using diamond-anvil cell (DAC) techniques at beamlines X17C and U2A of National Synchrotron Light Source (NSLS). The lattice parameters and unit-cell volumes were refined in Pm1 space group throughout the experimental pressure range. The anisotropy of lattice compression decreases with pressure due to a more compressible c axis and the compression becomes nearly isotropic in the pressure range of 10–25 GPa. The unit-cell volumes are fitted to the third-order Birch-Murnaghan equation of state, yielding K0 = 39.4(1.3) GPa, K0' = 8.4(0.4) for the bulk modulus and its pressure-derivative, respectively. No phase transition or amorphization was resolved from the X-ray diffraction data up to 29 GPa, however, starting from ~4 GPa, a new infrared vibration band (~3638 cm–1) 60 cm–1 below the OH stretching A2u band of brucite was found to coexist with the A2u band and its intensity continuously increases with pressure. The new OH stretching band has a more pronounced redshift as a function of pressure (–4.7 cm–1/GPa) than the A2u band (–0.7 cm–1/GPa). Comparison with first-principles calculations suggests that a structural change involving the disordered H sublattice is capable of reconciling the observations from X-ray diffraction and infrared spectroscopy studies.
Maining Ma, Wei Liu, Zhiqiang Chen, Zhenxian Liu, and Baosheng Li. Compression and structure of brucite to 31 GPa from synchrotron X-ray diffraction and infrared spectroscopy studies. American Mineralogist. 2013, 98, 1, 33-40.
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