High-pressure neutron diffraction study on H–D isotope effects in brucite

High-pressure neutron diffraction study on H–D isotope effects in brucite,10.1007/s00269-010-0372-5,Physics and Chemistry of Minerals,Juske HoritaAnto

High-pressure neutron diffraction study on H–D isotope effects in brucite   (Citations: 1)
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A neutron powder diffraction study of hydrogenated and deuterated brucite was conducted at ambient temperature and at pressures up to 9 GPa, using a Paris–Edinburgh high-pressure cell at the WAND instrument of the ORNL High Flux Isotope Reactor. The two materials were synthesized by the same method and companion measurements of neutron diffraction were conducted under the same conditions. Our refinement results show that the lattice-parameters of the a axis, parallel to the sheets of Mg–O octahedra, decrease only slightly with pressure with no effect of H–D substitution. However, the c axis of Mg(OD)2 is shorter and may exhibit greater compressibility with pressure than that of Mg(OH)2. Consequently, the unit-cell volume of deuterated brucite is slightly, but systematically smaller than that of hydrogenated brucite. When fitted to a third-order Birch–Murnaghan equation in terms of the normalized unit-cell volume, values of the bulk modulus for hydrogenated and deuterated brucite (K 0 = 39.0 ± 2.8 and 40.4 ± 1.3 GPa, respectively) are, however, indistinguishable from each other within the experimental errors. The measured effect of H–D substitution on the unit-cell volume also demonstrates that brucite (and other hydrous minerals) preferentially incorporate deuterium over hydrogen under pressure, suggesting that the distribution of hydrogen isotopes in deep-earth conditions may differ significantly from that in near-surface environments.
Journal: Physics and Chemistry of Minerals - PHYS CHEM MINER , vol. 37, no. 10, pp. 741-749, 2010
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    • ...Although brucite is regarded as having weak hydrogen bonds, Horita et al. (2010) recently reported an H–D isotope effect on the cell volume of brucite, based on neutron diffraction measurements of Mg(OH)2 and Mg(OD)2 up to 9 GPa...
    • ...This result contrasts with the case of Mg(OH)2: the unit cell volumes of Mg(OH)2 were systematically larger than those of Mg(OD)2 up to 9 GPa (Horita et al. 2010)...

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