Compression mechanism of brucite: An investigation by structural refinement under pressure

Abstract

Synchrotron X-ray powder diffraction study of brucite, Mg(OH) 2 , was carried out in a diamond anvil cell with an imaging plate detector from 0.6 to 18.0 GPa at room temperature using the angular-dispersive technique on beamline BL-18C at the Photon Factory, KEK, Japan. Using Rietveld analysis, unit-cell parameters as well as atomic positions of the O atoms in brucite have been successfully refined, taking into account the effects of preferred orientation. Variation of the c/a ratio with pressure indicates that the compression mechanism changes around 10 GPa, above which the compression behavior is isotropic. Based on the changes of the refined atomic positions of the O atoms with pressure, we conclude that the shortening of the interlayer distance controls compression below 10 GPa, whereas above this pressure compression of the oxygen sublattice is the dominant mechanism. Results of the structural refinements also suggest that the MgO 6 octahedral regularity initially approaches a regular configuration with pressure, which then remains unchanged above 10 GPa.

Vibrational spectroscopy and x-ray diffraction ofCd(OH)2to28G

“…13) (distinct from the amorphization observed in powder samples 11 ). Remarkable similarities were reported between the Raman spectra of the high-pressure phase of single-crystal Ca(OH) 2 and Sr(OH) 2 , and it is notable that the c/a ratio and many of bond lengths in Cd(OH) 2 are similar to those in Ca(OH) 2 (Table I). The spectra of the high-pressure phases of Cd(OH) 2 and Ca(OH) 2 are also closely similar: A sharper new peak appears on the high-frequency side of the A 1g (OH) mode during the phase transition in Ca(OH) 2 which is very similar to the new mode we observed near A 1g (OH) in Cd(OH) 2 (ν 7 in Fig.…”

“…This is mainly due to the fact that the O-H units are distant from each other along the a-axis, in comparison with the other hydroxides (see O-O in Table I). Among the transition-metal hydroxides (M = Ni, Co, Fe, Mn, and Cd), the magnitudes of the bond lengths and angle are the largest for Cd(OH) 2 (Table I). Therefore, it is of particular interest to compare the behavior of Cd(OH) 2 to Ca(OH) 2 and other transition-mental hydroxides under pressure.…”

Thermal expansion and compressibility in superconductingNaxCoO2∙4xD2OJorgensen1, Avdeev2, Hinks3 et al. 2005Phys. Rev. B6000View full textAdd to dashboardCite

“…Very similar behavior has been observed in the layered materials Mg(OH) 2 (brucite), [27] Mn ( It is tempting to use bond valence sum techniques [29] to estimate the change in the effective Ço oxidation state, based on the change in the Co-O bond length. Such calculations suggest a change in the Co oxidation state as large as 0.1 electrons over the 0.6 GPa pressure range of this study.…”

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

“…However, all of these measurements were conducted without a pressure transmitting medium [Meade and Jeanloz, 1990;Duffy et al, 1995], or with a rigid silicon oil medium [Nagai et al, 2000]. Ekbundit et al [1996] confirmed the amorphization in powder samples but reported a transition to a crystalline phase occurring at 6 GPa and room temperature in single crystal Ca(OH) 2 .…”