Abstract
A phase transition from Ca(OH)2 I (portlandite) to Ca(OH)2 II at high pressure and temperature has been confirmed, using in situ x-ray diffraction in a multianvil high pressure device (DIA). The structure was determined at 9.5 GPa and room temperature from data collected after heating the sample at 300°C at 7.2 GPa in a diamond anvil cell. Both the Le Bail fit and preliminary Rietveld refinement suggest that the new phase, which reverts to Ca(OH)2 I during pressure release, has a structure related to that of baddeleyite (ZrO1); it is monoclinic (P21/c) with a = 4.887(2), b = 5.834(2), c = 5.587(2), β = 99.74(2)°. The coordination number of Ca increases from six to seven (5 + 2) across the transition. At 500°C, the phase boundary is bracketed at 5.7 ± 0.4 GPa by reversal experiments performed in the DIA.
Original language | English (US) |
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Pages (from-to) | 311-319 |
Number of pages | 9 |
Journal | High Pressure Research |
Volume | 14 |
Issue number | 4-5 |
State | Published - 1996 |
Keywords
- Ca(OH)
- High pressure
- Phase transition
- X-ray diffraction
ASJC Scopus subject areas
- Condensed Matter Physics