High-pressure Raman Study Research Articles

High-pressure spectroscopic studies of europium gallium and gadolinium aluminum garnets

In this paper we report high-pressure Raman and mid-infrared studies of europium gallium garnet (Eu 3Ga 5O 12) and gadolinium aluminum garnet (Gd 3Al 5O 12). The europium/gadolinium garnets were studied up to 22/10 GPa using Raman spectroscopy and up to 15/22 GPa using infrared spectroscopy. The spectra do not show any clear phase transition over the investigated pressures for both the samples. However, for the case of Eu 3Ga 5O 12 the Raman modes broaden significantly beginning at about 12.5 GPa up to the highest pressure and remain broad even after quenching to atmospheric pressure.

Non-monotonic size dependence of the elastic modulus of nanocrystalline ZnO embedded ina nanocrystalline silver matrix

We present the first high pressure Raman study of nanocrystalline ZnO with differentaverage crystallite sizes. The problem of low Raman signals from nanometer-sized particleswas overcome by forming a nanocomposite of Ag and ZnO nanoparticles. The presence ofthe nanodispersed Ag particles leads to a substantial surface enhancement of the Ramansignal from ZnO. We find that the elastic modulus of nanocrystalline ZnO shows anon-monotonic dependence on the crystallite size and suggest that the non-monotonicityarises from an interplay between the elastic properties of the individual grains and theintergranular region.

High-pressure raman study on single crystalline methane hydrate surrounded by methane in a diamond anvil cell

High-pressure Raman measurements have been performed for single crystalline methane hydrate (MH) surrounded by fluid or solid methane in a diamond anvil cell. We successfully obtained the pure O-H stretching and lattice vibration spectra in MH-sI and MH-II phases. In these Raman spectra, there is no Raman band from water or ice-VI. The observed pressure of phase transformation from MH-sI to MH-II is 0.9 GPa, which is the same result as methane hydrate surrounded by water.

High pressure Raman studies of carbon nanotube materials

Raman spectroscopy is employed to study the pressure response of single-(SWCNTs), double- (DWCNTs) and multi-wall (MWCNTs) carbon nanotube materials. In DWCNTs, the outer tubes exhibit a similar pressure response to SWCNTs, where the tube sensitivity to pressure application is diameter dependent (higher for large diameter tubes). On the other hand, the inner tubes in DWCNTs and the innermost tubes in MWCNTs appear to be much less sensitive to pressure application, indicating the pressure screening inside the outer tubes. The pressure screening effect is strongly enhanced in MWCNTs.

High pressure Raman studies of carbon nanotube materials

Raman spectroscopy is employed to study the pressure response of single-(SWCNTs), double- (DWCNTs) and multi-wall (MWCNTs) carbon nanotube materials. In DWCNTs, the outer tubes exhibit a similar pressure response to SWCNTs, where the tube sensitivity to pressure application is diameter dependent (higher for large diameter tubes). On the other hand, the inner tubes in DWCNTs and the innermost tubes in MWCNTs appear to be much less sensitive to pressure application, indicating the pressure screening inside the outer tubes. The pressure screening effect is strongly enhanced in MWCNTs.

High-pressure Raman study of nano-channel materials: BaAl2Si2 and BaSi6

Structural phase transitions were explored for new nano-channel materials α-BaAl2Si2 and BaSi6 by means of high pressure Raman experiments, on the basis of the change in the Raman spectra which cover the frequencies from 40-600 cm-1. In spite of the structural similarity between BaSi6 and α-BaAl2Si2, the different behaviours were found under high pressure; for α-BaAl2Si2, there is an irreversible phase transition around 16-17 GPa, and for BaSi6 the reversible spectral change without distinct phase transition was observed up to 23 GPa.

High-pressure Raman study of nano-channel materials: BaAl2Si2and BaSi6

High-pressure Raman study of nano-channel materials: BaAl₂Si₂and BaSi₆

Pressure-induced helix—coil transition of poly-l-glutamic acid in water

The pressure effect on the helix-coil transition of aqueous poly-L-glutamic acid sodium salt (PLGA-Na) solutions was investigated by FT-IR spectroscopy. From the analysis of the amide I' band, the peak at 1637 cm-1 corresponding to the solvated α-helix structure increases with increasing pressure. The solvated α-helix structures of oligopeptides and proteins are stabilized upon compression. On the other hand, the peak intensities at 1710 and 1565 cm-1 corresponding to the C=O stretching mode of the COOH group and the C—O stretching mode of the COO-group of the side chain do not change with the pressure. According to high-pressure Raman study for the condensed aqueous CH3COONa solution, the pressure-induced dissociation of CH3COONa is found to be small. This result is qualitatively consistent with that of the side chain of PLGA-Na. The small pressure dependences of the side chain of PLGA-Na may be due to the high salt concentration in the solutions We have determined the difference in the partial molar volumes (PMV) between the α-helix and random coil structures of PLGA-Na at pD 5.0 to be +10.68±0.46 cm3/mol from the pressure dependence of the band intensities. The positive volume change of helix-coil transition of PLGA-Na is qualitatively consistent with the recent result of the volume change accompanying the helix—coil transition of PLGA (Noudeth G D et al, 2003 Biopolymers 70 563.).

Effects of pressure transmitting media on Raman features of single-walled carbon nanotubes

We have performed high pressure Raman studies of single-walled carbon nanotubes (SWCNTs) by using different organic solvents as the pressure transmitting medium (PTM). A linear dependence of pressure coefficient of Raman G band is found with the molecular weight of organic solvent. In addition, according to the experimental data and a comparative analysis of pressure measurement without the PTM, we explain the occurrence of plateau and hardening behavior of Raman G and D ∗ bands upon increasing pressure.

24aTG-11 構造I型Ga-Ge混晶クラスレートの高圧X線回折およびラマン散乱(クラスレート2,領域7,分子性固体・有機導体)

24aTG-11 構造I型Ga-Ge混晶クラスレートの高圧X線回折およびラマン散乱(クラスレート2,領域7,分子性固体・有機導体)

High-pressure Raman study on the decomposition of crystalline Cr(CO) 6

High-pressure Raman spectra (300–2200 cm −1) of crystalline Cr(CO) 6 at room temperature for pressures up to 29.5 GPa have been recorded. A probable second-order phase transition is assigned at ∼4.1 GPa. Recorded Raman spectra started to vanish at 20.8 GPa and upon further increase in pressures resulted in complete vanishing at 29.5 GPa. The dν/d p values suggest the breakdown of Dewar–Chatt–Duncanson model for the first time in homoleptic mono carbonyls which has been discussed. Decomposition of Cr(CO) 6 leads to the formation of polymeric CO with characteristic sp 2 carbon and (OCO) units for the first time.

Phase transitions in the H+-conducting perovskite ceramics by the quasi-elastic neutron and high-pressure Raman scattering

H+-containing lanthanide-doped perovskites A(Ba, Sr etc.)B(Zr, Ce, Ti etc.)O3 are potential ceramic membranes for fuel cell and medium temperature water electrolysis (300–800 °C). The comparison studies of the hydrated and non-hydrated Yb-doped BaZrO3 and SrZrO3 were performed by thermal expansion, medium–high temperature neutron and room-temperature high-pressure Raman scattering. Neutron diffraction and elastic/quasi-elastic studies carried out for BaZrO3 ceramic show the presence of the protons, their successive diffusion above ∼600 °C, and then their departure above 750 °C (under vacuum). Phase transitions and their modification by proton insertion are discussed. A high-pressure Raman study of SrZrO3 performed at room temperature in the diamond anvil cell reveals the presence of two pressure-induced phase transitions at about 5 and 22 GPa and confirms that proton insertion modifies the phase transition sequences.

Raman Spectroscopic Investigations of Pressure-Induced Phase Transitions in n-Hexane

We report high-pressure Raman studies on n-hexane up to 16 GPa. n-Hexane undergoes solid-solid transition around 9.1 GPa along with an already reported liquid-solid transition around 1.4 GPa. The intensity ratio of the Raman modes relating the all-trans conformation (1147 and 2872 cm-1) to that of the gauche conformation (1074 and 2923 cm-1) shows a sudden change across 9.1 GPa, suggesting an increase in the all-trans population conformers above 9.1 GPa. The disappearance of the torsional modes suggests a steric hindrance to the methyl end group, similar to the n-heptane case, suggesting that the high-pressure phase (above 9.1 GPa) is an orientationally disordered phase. In general, the transition pressure for the solid-solid transition is inversely proportional to the length of the carbon backbone in the medium chain length n-alkanes.

High pressure Raman study of the second‐order vibrational modes of single‐ and double‐walled carbon nanotubes

AbstractThe pressure response of the second‐order Raman G′ band of bundled double‐ (DWCNTs) and single‐wall carbon nanotubes (SWCNTs) has been investigated by means of Raman spectroscopy using the 632.8 nm excitation. The different pressure responses of the G′ peak in SWCNTs and its corresponding components associated with the inner and the outer tubes in DWCNTs can be attributed to the different diameters of the resonantly probed tubes and the strength of the inner‐outer tube interaction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High pressure Raman studies of dense nanocrystalline BaTiO3 ceramic

High pressure Raman spectra have been measured on 20 nm BaTiO3 ceramic from atmospheric pressure to 36.7 GPa. It was found that most of tetragonal phase has transformed to orthorhombic phase at about 10.9 GPa, and a new phase appeared at about 19.8 GPa. Raman modes still persisted up to 36.7 GPa. The phase transition was reversible.

Low-temperature single crystal X-ray diffraction and high-pressure Raman studies on [(CH 3) 2NH 2] 2[SbCl 5

The structure of bis(dimethylammonium) pentachloroantimonate(III), [(CH 3) 2NH 2] 2[SbCl 5], BDP, was studied at 15 K and ambient pressure by single-crystal X-ray diffraction as well as at ambient temperature and high pressures up to 4.87(5) GPa by Raman spectroscopy. BDP crystallizes in the orthorhombic Pnma space group with a=8.4069(4), b=11.7973(7), c=14.8496(7) Å, and Z=4; R 1=0.0381, w R 2=0.0764. The structure consists of distorted [SbCl 6] 3− octahedra forming zig-zag [{SbCl 5} n ] 2 n− chains that are cross-linked by dimethylammonium [(CH 3) 2NH 2] + cations. The organic and inorganic substructures are bound together by the N–H…Cl hydrogen bonds. The distortions of [SbCl 6] 3− units increase, partly due to the influence of the hydrogen bonds which became stronger, with decreasing temperature. The preliminary room temperature, high-pressure X-ray diffraction experiments suggest that BDP undergoes a first-order phase transition below ca. 0.44(5) GPa that destroys single-crystal samples. The transition is accompanied by changes in the intensities and positions of the Raman lines below 400 cm −1.

Pressure-induced change in the compressional behavior of the O-H bond in chrysotile: A Raman high-pressure study up to 4.5 GPa

A change in the linear pressure behavior of the chrysotile Raman O-H band is revealed by an in-situ high-pressure Raman study using a diamond anvil cell (DAC) at 0.1–0.4 GPa pressure intervals. The peak of 3701 cm −1 can be accurately determined in the pressure range of 0.2–4.5 GPa regardless of peak fitting models. The pressure ( P )-wavenumber (ν) relationship for the peak is closely approximated by two linear functions with the slopes (dν/d P ) of 4.3 cm −1 /GPa and 1.7 cm −1 /GPa at pressures above and below 1.7 GPa, respectively. The spectral resolution given by a peak fitting method (0.5 cm −1 ) implies that these functions for changes in the positions of the 3701 cm −1 peak provide pressure estimates with resolutions of 0.1–0.2 GPa. This method can be used to estimate remnant pressure in natural samples in the form of thin sections. The pressure shift characterized by the change in slope and the associated decrease of the peak width can be explained by a model where the change in compressibility of the tetrahedral layer affects the interaction between the inner O-H and Si atoms forming a six-membered ring. The high-pressure dependence at pressures lower than 1.7 GPa may be a contribution of a dominant layer-parallel (in-plane) compression that compensates a distortion in the tetrahedral layer of chrysotile. The conclusion that chrysotile changes its compressibility at around 1.7 GPa is significant for understanding of the properties of chrysotile nano-fibers and possibly for thermodynamic consideration on serpentine phase relations.

High-pressure Raman study on the guest vibration in the host cage of methane hydrate structure I

High-pressure Raman scattering measurements for the structure I of methane hydrate (MH) and methane deuterohydrate (MDH) have been performed at 296 K in order to observe the vibration of guest methane molecule in the host water cage. An analysis of the peak frequencies of the lattice vibrations of MH and MDH shows that the guest vibration in the large cage appears at ∼50 cm −1, being based on the clear distinction between the guest and host vibrations by deuteration of the host cage.

High-pressure Raman study of Ba doped type-III germanium clathrate Ba24Ge100 up to 26 GPa

High-pressure Raman measurements of type-III germanium clathrate Ba24Ge100 have been made up to 26 GPa at room temperature. We observed low-frequency vibrational (rattling) modes associated with guest Ba atoms at 25–50 cm−1, and host Ge framework vibrations around 50–250 cm−1, which are compared with those of silicon clathrate Ba24Si100. High-pressure phase transition was found at 3.2 GPa, which seems to be due to the structural distortion combined with the enhanced guest-host interactions. Ba24Ge100 becomes irreversibly amorphous at pressures above 22 GPa. This pressure is less than that of type-I Ba8Ge43 clathrate, indicating that type-III structure is less stable than type-I Ge clathrate under high pressures.

Vibrational and elastic properties of hcp barium under pressure and their relation to its electronic structure

High-pressure Raman studies of both hexagonal-close-packed phases Ba-II and Ba-V are reported. Combining the E 2 g phonon data with the existing equation of state data, the pressure dependence of the elastic shear modulus C 44 has been derived. The pressure shift of the E 2 g mode in both phases is discussed in terms of the elastic parameters. Though the pressure response of the observed Raman mode shows normal behaviour in both phases, more subtle differences can be traced back to differences of the electronic structure in both phases.