High-pressure Raman and Brillouin studies of single crystalline gas hydrates

2003 ◽  
Vol 81 (1-2) ◽  
pp. 127-133 ◽  
Author(s):  
H Shimizu
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Brillouin Scattering ◽  
Low Frequency ◽  
Visual Observation ◽  
Cage Structure ◽  
Two Phase ◽  
Single Crystalline ◽  
Open Structures ◽  
Diamond Anvil

Methane hydrate (MH) and argon hydrate (AH) single crystals were synthesized in a diamond anvil cell to investigate their intrinsic high-pressure properties by visual observation and in situ Raman and Brillouin-scattering measurements. Single crystalline MH shows clearly two phase transitions at P =0.9 and 1.9 GPa in its crystalline shape and state under a microscope, and in the change in its Raman spectra of C–H stretching vibrations of guest CH4 molecules. The first determination of the elastic properties in MH sI phase has revealed that MH is about 10% softer than the most common ice Ih, which is accounted for by MH's void-rich and open structures. For a single-crystal AH, we have observed two phase transitions from AH-I (sII) to AH-II at about P =0.65 GPa and from AH-II to AH-III at P =1.02 GPa. The breakdown of the cage structure in AH-III was confirmed by the disappearance of the O–H stretching mode of host H2O lattices. The possibility of Ar double occupancy in the large cages of sII and higher pressure phases is investigated by the low-frequency Raman peak observed around 120 ~ 140 cm–1 in view of recent MD calculations. PACS Nos.: 62.30+d, 62.50+p, 62.65+k, 64.70-p, 78.30-j, 78.35+c

PHASE TRANSITION IN LAYERED PEROVSKITE LIKE MANGANATE Ca3Mn2O7 UNDER HIGH PRESSURE

2001 ◽  
Vol 15 (18) ◽  
pp. 2491-2497 ◽  
Author(s):  
J. L. ZHU ◽  
L. C. CHEN ◽  
R. C. YU ◽  
F. Y. LI ◽  
J. LIU ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Diamond Anvil Cell ◽  
The Other ◽  
Layered Perovskite ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
Diamond Anvil

In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca 3 Mn 2 O 7 under pressures up to 35 GPa have been performed by using diamond anvil cell with synchrotron radiation. The results show that the structure of layered perovskite-like manganate Ca 3 Mn 2 O 7 is unstable under pressure due to the easy compression of NaCl-type blocks. The structure of Ca 3 Mn 2 O 7 underwent two phase transitions under pressures in the range of 0~35 GPa. One was at about 1.3 GPa with the crystal structure changing from tetragonal to orthorhombic. The other was at about 9.5 GPa with the crystal structure changing from orthorhombic back to another tetragonal.

Observation of pressure-induced electron transfer in SnC2O4

2021 ◽  
Author(s):  
Michael Pravica ◽  
Roman Chernikov ◽  
Kevin Ayala Pineda ◽  
Jianbao Zhao ◽  
Petrika Cifligu ◽  
...  
Keyword(s):  
High Pressure ◽  
Electron Transfer ◽  
Phase Transitions ◽  
Absorption Spectroscopy ◽  
Diamond Anvil Cell ◽  
X Ray ◽  
Pressure Behavior ◽  
Diamond Anvil ◽  
X Ray Absorption

We examined the high pressure behavior of stannous oxalate via Raman and x-ray absorption spectroscopy (XAS) inside a diamond anvil cell. Phase transitions were observed to occur near 2.6 and...

scholarly journals Effects of Composition, Pressure, and Temperature on the Elastic Properties of SiO2–TiO2 Glasses: An Integrated Ultrasonic and Brillouin Study

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 481
Author(s):  
Murli H. Manghnani ◽  
Quentin Williams ◽  
Teruyuki Matsui ◽  
Peter C. Schultz ◽  
Charles R. Kurkjian
Keyword(s):  
High Pressure ◽  
Elastic Properties ◽  
Excellent Agreement ◽  
Diamond Anvil Cell ◽  
Brillouin Scattering ◽  
Elastic Behavior ◽  
Tio2 Content ◽  
Diamond Anvil ◽  
Raman Study ◽  
Low Pressures

We have systematically investigated the elastic properties (ρ, VP, VS, K, μ and σ) of eight SiO2–TiO2 glasses, varying in composition from 1.3 to 14.7 wt% TiO2, as a function of pressure up to 0.5 GPa by the pulse superposition (PSP) ultrasonic technique, and two compositions (1.3 and 9.4 wt% TiO2) up to ~5.7 GPa by Brillouin scattering in a diamond anvil cell. The parameters were also measured after annealing to 1020 °C. Composition–elasticity relationships, except for K and σ, are more or less linear; the annealing simply makes the relationships more uniform (less scatter). There is excellent agreement between the ultrasonic and Brillouin measurements at ambient and high pressure. The pressure-induced anomalous elastic behavior (negative dVP/dP and dK/dP) becomes more negative (more compressible) with the increasing TiO2 content. Correspondingly, the acoustic Grüneisen parameters become more negative with increases in the TiO2 content, reaching a minimum near ~8–10 wt% TiO2. The comparison of the low- and high-pressure ultrasonic and Brillouin VP and VS in two glasses (1.3 and 9.4 wt% TiO2) shows excellent agreement, defining the reversible elastic behavior at low pressures and irreversible behavior at higher pressures (≥5.7 GPa) well. This result is consistent with our previous high-pressure Raman study showing an irreversible structural change in a similar pressure range.

Phase transitions in Al2(WO4)3: high pressure investigations of low frequency dielectric constant and crystal structure

2004 ◽  
Vol 16 (41) ◽  
pp. 7321-7330 ◽  
Author(s):  
G D Mukherjee ◽  
V Vijaykumar ◽  
S N Achary ◽  
A K Tyagi ◽  
B K Godwal
Keyword(s):  
Crystal Structure ◽  
Dielectric Constant ◽  
High Pressure ◽  
Phase Transitions ◽  
Low Frequency

The Theoretical Study of the Cinnabar-to-Rocksalt Phase Transitions of HgTe and CdTe under High Pressure

2014 ◽  
Vol 1004-1005 ◽  
pp. 1608-1614 ◽  
Author(s):  
Xi Duo Hu ◽  
De Hai Zhu ◽  
Zhi Feng Zeng ◽  
Shao Rui Sun
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Theoretical Study ◽  
Chain Structure ◽  
Two Phase ◽  
Principle Calculation ◽  
First Principle Calculation ◽  
First Order ◽  
Rocksalt Phase

We performed the first-principle calculation to study the structures of cinnabar phase and the Cinnabar-to-rocksalt Phase transitions of HgTe and CdTe under high pressure. The calculated results show that for HgTe, the zincblende-to-cinnabar phase transition is under 2.2GPa, and the cinnabar-to-rocksalt phase transition is under 5.5 GPa; For CdTe, the two phase transitions occur under 4.0 GPa and 4.9 GPa, respectively, which well agree with the experimental results. The cinnabar-to-rocksalt phase transitions of most compounds, including HgTe and CdTe, except HgS are of first-order, and it is due to that their cinnabar phases are not chain structure as HgS and there are no relaxation process before the phase transition.

High-pressure experimental study on Rb2S: antifluorite to Ni2In-type phase transitions

2011 ◽  
Vol 67 (2) ◽  
pp. 109-115 ◽  
Author(s):  
David Santamaria-Perez ◽  
Angel Vegas ◽  
Claus Muehle ◽  
Martin Jansen
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Type Structure ◽  
Gradual Transition ◽  
Structural Behaviour ◽  
Two Phase ◽  
Band Maximum ◽  
X Ray ◽  
Type Phase ◽  
Strong Luminescence

The high-pressure behaviour of dirubidium sulfide, Rb2S, with antifluorite-type structure under room conditions (space group Fm\bar 3 m) has been studied up to 8 GPa at room temperature using angle-dispersive X-ray powder diffraction in a diamond–anvil cell (DAC). X-ray measurements have allowed us to completely characterize two phase transitions upon compression: (i) to an anticotunnite-type structure (Pnma) at some pressure between 1 bar and 0.7 GPa, and (ii) to a Ni2In-type structure (P63/mmc) at 2.6 GPa. A gradual transition from the Pnma to the P63/mmc structures seems to occur between 2.6 and 4.5 GPa. These results are in excellent agreement with previous theoretical predictions. Strong luminescence is observed above 2.6 GPa (band maximum at 703 nm) when the transition to the Ni2In-type phase starts to occur, the band maximum showing a non-linear blue shift with pressure. The observed sequence of phase transitions in Rb2S is discussed in relation to the high-pressure structural behaviour of isomorphic sulfides and the structures are compared with the cationic arrays of their corresponding oxides (e.g. rubidium sulfate, in which the sulfide has been oxidized).

Measurement of Physical Properties of Lubricants Under High Pressure by Brillouin Scattering in a Diamond Anvil Cell

1995 ◽  
Vol 117 (3) ◽  
pp. 519-523 ◽  
Author(s):  
Y. Nakamura ◽  
I. Fujishiro ◽  
K. Nishibe ◽  
H. Kawakami
Keyword(s):  
High Pressure ◽  
Shear Modulus ◽  
Sound Velocity ◽  
Diamond Anvil Cell ◽  
Brillouin Scattering ◽  
Transverse Mode ◽  
Thermodynamic Relation ◽  
Slope Change ◽  
Scattering Spectra ◽  
Diamond Anvil

Brillouin scattering spectra and their transverse mode were measured for paraffinic and naphthenic synthetic lubricants, employing a high-pressure diamond anvil cell (DAC). Sound velocity, density, refractive index, and shear modulus under high pressure were obtained. The density obtained from the thermodynamic relation was compared with that from Lorentz-Lorenz‘s formula. The densities were also compared with Dowson‘s density-pressure equation of lubricants. The sound velocity in the transverse mode and shear modulus were obtained for 5P4E up to 2.7 GPa. A slope change in the pressure-sound velocity diagram was confirmed at about 0.3 GPa, which may be associated with crystallizaton of 5P4E, observed through a diamond optical window in the DAC.

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