The baddeleyite-type high pressure phase of Ca(OH)2 |
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| Authors: | M Kunz K Leinenweber J B Parise T-C Wu W A Bassett K Brister |
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| Institution: | 1. CHiPR and Department of Earth and Space Sciences , State University of New York , Stony Brook, NY, 11794-2100;2. Department of Chemistry , Arizona State University , Tempe, AZ, 85287-1604;3. Mineral Physics Laboratory, Department of Geological Sciences, Cornell University , Ithaca, NY, 14853;4. Cornell High Energy Synchrotron Source, Wilson Lab, Cornell University , Ithaca, NY, 14853 |
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| Abstract: | 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), 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. |
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| Keywords: | Ca(OH)2 phase transition x-ray diffraction high pressure |
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