A crystalline‐to‐crystalline phase transition in Ca(OH)₂ at 8 GPa and room temperature

Abstract

X‐ray diffraction and Raman spectroscopy measurements reveal that Ca(OH)2‐portlandite transforms to a crystalline phase with an ordered OH sublattice between 8 and 14 GPa at room temperature under quasi‐hydrostatic stress conditions in an Ar pressure medium. The amorphization previously reported at 11 GPa under no pressure medium was not observed up to 26 GPa. The width and separation of the fluorescence peaks from the ruby chips embedded in Ca(OH)2 without a medium suggest that deviatoric stress is responsible for the previously observed amorphization. Our study demonstrates that the behavior of hydrous phases in the subducting slab could be sensitive to local deviatoric stresses. Together with similar reports on quartz, our observation on Ca(OH)2 indicates that deviatoric stress is an important factor to consider for P‐induced amorphization reported in a wide range of materials.

Equation of state, phase stability, and amorphization ofSnI4at high pressure and temperature

“…18 The variation in amorphization pressures among our samples may also be due to subtle differences in the deviatoric stresses between samples. Catalli et al 17 have found the pressure-induced amorphization of Ca͑OH͒ 2 is likely facilitated by nonhydrostatic ͑deviatoric͒ stress and they do not observe this transition in a quasihydrostatic pressure medium ͑argon͒. Although the nonhydrostatic stresses in our system appear to be relatively low ͑Ͻ0.5 GPa at 20 GPa͒, tin iodide may be extremely sensitive to even small deviatoric stresses that change the amorphization pressure by up to several gigapascals.…”

“…The weak intermolecular forces in tin iodide may make it sensitive to even small deviatoric stresses, which can change the amorphization pressure of crystals. 17 At pressures above 15 GPa, all samples appear to behave about the same, apparently due to a more uniform stress environment from sample to sample. Table II.…”

The postspinel boundary in pyrolitic compositions determined in the laser‐heated diamond anvil cell

“…In order to prevent capturing of H 2 O, the loading was conducted in a dry Ar chamber where the Ar gas pressure was maintained higher than the atmospheric pressure throughout the procedure. In Raman scattering measurements, no detectable amount of H 2 O has been found in an Ar medium [e.g., Catalli et al , ].…”

“…In order to prevent capturing of H 2 O, the loading was conducted in a dry Ar chamber where the Ar gas pressure was maintained higher than the atmospheric pressure throughout the procedure. In Raman scattering measurements, no detectable amount of H 2 O has been found in an Ar medium [e.g., Catalli et al, 2008]. Synchrotron X-ray diffraction (XRD) patterns were measured in situ at high P-T in double-sided LHDAC at beamline 13-IDD of the GeoSoilEnviroConsortium for Advanced Radiation Sources (GSECARS) sector and beamline 16-IDB of the High Pressure Collaborative Access Team (HPCAT) sector [Meng et al, 2006] at the Advanced Photon Source.…”

Portlandite crystal: Bulk, bilayer, and monolayer structures

“…At each corner of an octahedron, each O atom binds one H atom and the latter interacts with three neighboring hydroxyl groups of the adjacent layer. Early studies on bulk AEMHs revealed that the application of temperature and pressure may result in dramatical changes in their crystal structure and their electronic properties [11][12][13][14][15][16][17][18]. Moreover, early theoretical studies showed the reliability of the use of first principles calculations with a plane-wave basis set in combination with the generalized gradient approximation exchange-correlation functional for the investigation of structural and electronic properties of these materials [19][20][21][22].…”