Pressure responses of portlandite and H–D isotope effects on pressure-induced phase transitions |
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| Authors: | Riko Iizuka Hiroyuki Kagi Kazuki Komatsu Daichi Ushijima Satoshi Nakano Asami Sano-Furukawa Takaya Nagai Takehiko Yagi |
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| Institution: | (1) Geochemical Research Center, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan;(2) National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan;(3) Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirane Shirakata, Tokai-mura, Ibaraki 319-1195, Japan;(4) Division of Earth and Planetary Sciences, Graduate School of Sciences, Hokkaido University, Sapporo 060-0810, Japan;(5) Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan |
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| Abstract: | The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature
from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic
conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization)
observed from the Raman and IR spectra of Ca(OH)2 occurred at lower pressures than those of Ca(OD)2. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns.
X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization
in a helium pressure medium within the examined pressure region. These results suggest that the H–D isotope effect is engendered
in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol–ethanol pressure medium (i.e.,
packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines,
even at pressures below the hydrostatic limit of the pressure medium. |
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