Spectroscopic Study of the Effects of Pressure Media on High-Pressure Phase Transitions in Natrolite

Abstract

Structural phase transitions in natrolite have been investigated as a function of pressure and different hydrostatic media using micro-Raman scattering and synchrotron infrared (IR) spectroscopy. Natrolite undergoes two reversible phase transitions at 0.86 and 1.53 GPa under pure water pressure medium. These phase transitions are characterized by the changes in the vibrational frequencies of four-and eight-membered rings related to the variations in the bridging T-O-T angles and the geometry of the elliptical eight-ring channels under pressure. Concomitant to the changes in the framework vibrational modes, the number of the O-H stretching vibrational modes of natrolite changes as a result of the rearrangements of the hydrogen bonds in the channels caused by a successive increase in the hydration level under hydrostatic pressure. Similar phase transitions were also observed at relatively higher pressures (1.13 and 1.59 GPa) under alcohol-water pressure medium. Furthermore, no phase transition was found up to 2.52 GPa if a lower volume ratio of the alcohol-water to natrolite was employed. This indicates that the water content in the pressure media plays a crucial role in triggering the pressure-induced phase transitions in natrolite. In addition, the average of the mode Gru ¨neisen parameters is calculated to be about 0.6, while the thermodynamic Gru ¨neisen parameter is found to be 1.33. This might be attributed to the contrast in the rigidity between the TO 4 tetrahedral primary building units and other flexible secondary building units in the natrolite framework upon compression and subsequent water insertion.

Stability and phase transition of nanoporous rutile TiO2 under high pressure

“…The results show that the transition from nanoporous rutile phase to the baddeleyite phase takes place at a pressure of y10.8 GPa. The onset phase transition pressure is lower than that of y30 nm rutile nanoparticles (y8.7 GPa) but lower than that of y10 nm rutile nanoparticles (y20 GPa) and bulk material (12)(13). The rutile phase transforms into the baddeleyite phase completely beyond 26.1 GPa, but with poor crystallinity.…”

“…Recently, a high-pressure technique has been employed to study nanoporous materials. [11][12][13][14] Mechanical properties of the dense zinc framework Zn(Im) 2 and its lithiumboron analogue LiB(Im) 4 have been compared by using high-pressure synchrotron X-ray diffraction, nanoindentation and density functional calculations. 11 Porous metal-organic frameworks (MOFs) such as Zn(2-methylimidazole) 2 (ZIF-8) have been investigated under modest and industrially accessible pressures (y1 GPa), which indicated ZIF-8 is highly compressible with an irreversible pressure-induced amorphization at low pressures.…”

Acoustic and elastic properties of silicone oil under high pressure

“…[9][10][11][12][13][14][15][16][17][18] Because nonhydrostatic conditions have impact on structural or electronic transitions of matter under high pressure, various PTMs have been investigated and their hydrostaticity is focused on, such as silicone oil. [6][7][8] For example, Piermarini et al studied the hydrostatic limits in silicone oil as well as other liquid and solid PTMs. 19 Ragan et al reported a preliminary investigation on the hydrostaticity for the Dow Corning 200 silicone uid.…”

Spectroscopic characterization of alkali-metal exchanged natrolites

“…Recently, Kolesov and Geiger (2006) reported the dehydration behavior of natrolite by in situ high-temperature Raman measurements. They observed that all the O-H bands become gradually broader and weaker with increasing temperature up to 570 K. On the other hand, the effect of the increase in the structural water content during the formation of the ordered-paranatrolite and superhydrated natrolite under hydrostatic pressure has been studied using Raman and IR methods (Demontis et al 2005;Liu et al 2010).…”