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1.
The dissociation of methane hydrate at high pressure is studied by in situ Raman spectroscopy in a diamond-anvil cell. As for the Raman spectrum of sI methane hydrate, the v(1) band of CH(4) is split into two peaks v'(1) and v'(1), indicating the partitioning of CH(4) between the large (5(12)6(2)) and small (5(12)) cavities, respectively. With increasing temperature, the intensity ratio of Iv'(1)/Iv'(1) decreases obviously, and the d(Iv'(1)/Iv'(1))/dT is -0.079 K(-1). Additionally, the v(1) band of the dissolved CH(4) is close to v'(1) of the CH(4) molecule engaged in the small 5(12) cavity. This implies that, in the initial stage of hydrate formation, the abundance of small 5(12) cavities is greater than that of large 5(12)6(2) cavities. 相似文献
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The Raman spectroscopy of n-pentane was investigated in a Moissanite anvil cell from 0.07 GPa to 4.77 GPa at ambient temperature. The result shows that the CH3 symmetric stretching vibration (2877 cm(-1)) and asymmetric stretching vibration (2964 cm(-1)), the CH2 symmetric stretching vibration (2856 cm(-1)) and asymmetric stretching vibration (2935 cm(-1)), and -(CH2)n- in-phase twist mode (1303 cm(-1)) shifted to higher wavenumbers almost linearly with increasing pressure. Around 2.4 GPa an abrupt visible change took place, indicating a sort of phenomenon of freezing due to over-pressurization. In the pressure range of 2.84 to 4.77 GPa a high-pressure phase transition may occur in the crystallized n-pentane. By determining pressure with the method of solid-liquid coexistence, we concluded that the equilibrium freezing pressure of n-pentane is 1.90 +/- 0.05 GPa at 27 degrees C. 相似文献
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The superconducting transition temperature of single-crystal and polycrystal uranium has been determined as a function of hydrostatic pressure to 24 kbar. Although the general form of theT
c
(P) variation is similar for the two types of material, features are present in the detailed behavior for the single-crystal samples which are not found for polycrystal samples. These features are presumed to be associated with the first-order transitions observed at zero pressure. A low-temperature phase diagram has been constructed and the electronic nature of the various phases is discussed.Research sponsored by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under AFOSR contract no. AFOSR-F44620-72-C-0017.Work performed under the auspices of the U.S. Atomic Energy Commission. 相似文献
4.
Mustafa Uludoğan Tahir ÇağIn Alejandro Strachan William A. Goddard III 《Scientific Modeling and Simulation》2001,8(2-3):193-202
We use ab-initio Quantum Mechanics to study the zero temperature phase diagram of BaO. We calculate zero temperature Equations of State of different crystalline phases [B1 (NaCl), B8(NiAs), B2(CsCl), and distorted B2] using Density Functional Theory (DFT) with the generalized gradient approximation (GGA). We find the B1 structure to be the thermodynamically stable one at zero pressure; followed by three pressure induced phase transitions. We find that at P=11.3 GPa BaO transforms from B1 to B8; at P=21.5 GPa from B8 to distorted B2. The distorted B2 phase continuously approaches the B2 structure, the phase transformation occurs at P=62 GPa. We also study the band structure of BaO in its high pressure (B2) phase. For P=60.5 GPa, we find a band gap of 3.5 eV in agreement with experimetal value. We find metallization at P=230.6 GPa. 相似文献
5.
Teruhisa Hongo Ken-ichi Kondo Kazutaka G. Nakamura Toshiyuki Atou 《Journal of Materials Science》2007,42(8):2582-2585
High pressure Raman spectroscopic study of Sm2O3 poly crystal was performed up to 21.0 GPa and room temperature using a diamond anvil cell. Pressure induced phase transition
was observed at 2.6 GPa in the pressure increasing process. This phase transition corresponds to the monoclinic B type phase
→ the hexagonal A type transformation. The A type phase was stable up to 21.0 GPa. In the pressure release process, the A
type phase was stable above 1.8 GPa, and was completely reverted to the B type phase at 1.1 GPa. The phase transition was
confirmed to be reversible with a hysteresis of approximately 1.0 GPa. 相似文献
6.
The selenium nanowires with diameter of 70 nm and length of 40 μm were synthesized by a facile solution method. High-pressure behavior of Se nanowires has been investigated by in situ Raman scattering up to 20.2 GPa at room temperature. A reversible phase transition from hexagonal to monoclinic occurs at 18.1 GPa. This transition pressure is higher than that of 14.0 GPa for bulk Se. The intrinsic geometry and/or the increasing energy band gap of Se nanowires are considered to contribute to the increase of transition pressure. 相似文献
7.
Mustafa Uludoan Tahir ?aIn Alejandro Strachan William A. Goddard III 《Journal of Computer-Aided Materials Design》2001,8(2-3):193-202
We use ab-initio Quantum Mechanics to study the zero temperature phase diagram of BaO. We calculate zero temperature Equations of State of
different crystalline phases [B1 (NaCl), B8(NiAs), B2(CsCl), and distorted B2] using Density Functional Theory (DFT) with
the generalized gradient approximation (GGA). We find the B1 structure to be the thermodynamically stable one at zero pressure;
followed by three pressure induced phase transitions. We find that at P=11.3 GPa BaO transforms from B1 to B8; at P=21.5 GPa from B8 to distorted B2. The distorted B2 phase continuously approaches the B2 structure, the phase transformation
occurs at P=62 GPa. We also study the band structure of BaO in its high pressure (B2) phase. For P=60.5 GPa, we find a band gap of 3.5 eV in agreement with experimetal value. We find metallization at P=230.6 GPa.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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Bo Kong Ti-Xian Zeng Zhu-Wen Zhou De-Liang Chen Xiao-Wei Sun 《Bulletin of Materials Science》2014,37(3):549-552
The structure and pressure-induced phase transitions for CdSe are investigated using first-principles calculations. The pressure-induced phase transition sequence WZ/ZB → Rs → Cmcm → CsCl for CdSe is drawn reasonably for the fist time, the corresponding transition pressures are 3.8, 29 and 107 GPa, respectively and the intermediate states between the Cmcm structure and the CsCl structure should exist. 相似文献
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Optical-trapping confocal Raman microscopy enhances the capabilities of traditional Raman spectroscopy for the analysis of small particles by significantly reducing the sampling volume and minimizing background signal from the particle surroundings. Chemical composition and structural information can be obtained from optically trapped particles in aqueous solution without the need for labeling or extensive sample preparation. In this work, the challenges of measuring temperature dependent changes in suspended particles are addressed with the development of a small-volume, thermally conductive sample cell attached to a temperature-controlled microscope stage. To demonstrate its function, the gel to liquid-crystalline phase transitions of optically trapped lipid vesicles, composed of pure 1,2-ditridecanoyl-sn-glycero-3-phosphocholine (DTPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), were detected by changes in Raman spectra of the lipid bilayer. The Raman scattering data were found to correlate well with differential scanning calorimetry (DSC) results. 相似文献
14.
Ryuichiro Oshima Fuminobu Hori Yasunori Kibata Masao Komatsu Michio Kiritani 《Materials Science and Engineering: A》2003,350(1-2):139-144
Fe–Rh alloys of Rh concentrations ranging from 40 to 50at.% and of B2 phase were deformed by use of a compression machine capable of running tests at high speeds of impact. Induced complicated substructures and phases were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and positron annihilation spectroscopy (PAS). A characteristic arrangement of L10 domains was observed, along with very small transformed A1 domains and dispersed in the residual B2 matrix. On the basis of the experimental results, we suggest a coupling of a pair of shears along {112}11−1B2 for the transformation mechanisms from B2 to L10 and A1 phases. 相似文献
15.
Perchlorate (ClO4-) has recently emerged as a widespread environmental contaminant found in groundwater and surface water, and there is a great need for rapid detection and monitoring of this contaminant. In this study, we explore the use of surface-enhanced (SERS) and normal Raman spectroscopy for detecting ClO4- at low concentrations. We found that ClO4- is SERS active and, for the first time, were able to detect ClO4- at concentrations as low as 10(-6)-10(-7) M (or 10-100 microg/L) through the application of silver SERS substrates or selective sorbents such as bifunctional anion-exchange resins. The use of selective sorbents greatly enhanced the reproducibility and sensitivity of ClO4- detection by normal Raman spectroscopy. Further exploration and research may allow application of these techniques for in situ, real-time detection and monitoring of ClO4- in environmental samples at even lower concentrations. 相似文献
16.
P.I. PolyakovV.V. Slyusarev S.M. Konoplyuk V.V. KokorinYu.S. Semenova 《Materials Letters》2012,67(1):263-265
In this paper dependences of characteristic temperatures on hydrostatic pressure for intermartensitic and martensitic transformations in Ni-Mn-Ga alloy are presented. In particular, intermartensitic transformation from martensitic phase with seven-layers periodicity to nonmodulated martensitic phase was studied by measurements of electrical resistivity under pressure. On the basis of these data an estimate of the transformation volume effect was made. It was found that transformation volume effect of intermartensitic transformation is an order of magnitude lower than that of martensitic transformation in this alloy. 相似文献
17.
Phase transitions in LiKSO4 have been visually observed in a diamond-anvil cell up to 16 GPa. The observations confirm a symmetry change at 0·9 GPa and
a solidstate crystal to amorphous transition at 12 GPa. The crystal exhibits a memory across the crystalline transitions.
Interesting microstructural features were observed in the range of the amorphous phase. 相似文献
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K. B. Panfilovich P. I. Budarin V. V. Sagadeev V. A. Glinkin 《Journal of Engineering Physics and Thermophysics》1995,68(2):237-241
An analysis of experimental investigations of the radiative characteristics of solid and liquid bodies and real gases in the vicinity of phase transitions is presented.Kazan State Technological University. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 2, pp. 271–275, March–April, 1995. 相似文献
20.
Two new high temperature anomalies at 511 K and 538 K in CsCuCl3 were investigated using different techniques such as differential thermal analysis, differential scanning calorimetry, thermal expansion, and reflectance measurements. These anomalies together with the Jahn-Teller effect of the copper ions suggest that these phase transitions can be explained as a Jahn-Teller induced transition in the case of an antiferro-distortive ordening. 相似文献