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51.
V. Malathy Devi D. Chris Benner A. Predoi-Cross 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(16):2355-2369
The McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory (NSO) on Kitt Peak, Arizona, was used to record infrared high resolution absorption spectra of CO2 spectra broadened by O2. These spectra were analyzed to measure O2-broadened half-width coefficients, O2-induced pressure-shift coefficients and speed dependent parameters for transitions in the 30013←00001 and 30012←00001 bands of 16O12C16O located near 6227 and 6348 cm−1, respectively. All spectra were obtained at room temperature using the long path, 6 m base path White cell available at NSO. A multispectrum nonlinear least-squares fitting algorithm employing Voigt line shapes modified to include line mixing and speed dependence was used to fit simultaneously a total of 19 spectra in the 6120-6280 cm−1 (30013←00001) and 6280-6395 cm−1 (30012←00001) spectral regions. 16 of the 19 spectra analyzed in this work were self broadened and three spectra were lean mixtures of CO2 in O2. The volume mixing ratios of CO2 in the three spectra varied between 0.06 and 0.1. Lorentz half-width and pressure-induced shift coefficients were measured for all transitions in the P(50)-R(50) range in both vibrational bands. The results obtained from present analysis have been compared with measurements available in the literature for self-, air-, oxygen- and argon-broadening. No significant differences were observed between the broadening and shift coefficients of the two bands. The N2-broadened half-width and pressure-shift coefficients were computed from measured air- and O2-broadened width and shift coefficients. 相似文献
52.
53.
Tomohiro Iwasaki Maiko Takahara Ryoichi Sonoda Satoru Watano 《Particle & Particle Systems Characterization》2007,24(3):236-241
This paper details an investigation into the enhancement of the water dissolution rate of mefenamic acid (MA) by means of a dry grinding treatment. The physico‐chemical properties of the ground MA particles were analyzed by measurements of specific surface area, powder X‐ray diffraction patterns, differential scanning calorimetry thermograms and infrared spectra, and the effects of the change in the physico‐chemical properties (especially, crystalline structure) on the dissolution rate were studied. The polymorphic transition from Form I (original) to II and the change of the molecular structure of MA did not occur in the grinding treatments. However, the specific surface area of the MA particles increased, and the crystallinity decreased (i.e., the amorphization level increased) as the grinding progressed. Hydrogen bonds formed between the carboxyl groups of the opposed asymmetric MA molecules were broken gradually after the grinding limit was attained in the grinding system, resulting in an effective improvement of the initial dissolution rate. 相似文献
54.
High pressure Raman spectroscopic studies on Gd2(MoO4)3(GMO) have been carried out at ambient temperature in the diamond cell to 10 GPa hydrostatic pressure. These experiments have
revealed pressure-induced phase transitions in GMO near 2 GPa and 6.0 GPa. The first transition is from Pba2(β′) phase to another undetermined crystalline phase, designated as phase II, and the second transition is to an amorphized
state. On releasing pressure there is a partial reversion to the crystalline state. The Raman data indicate that the amorphization
is due to disordering of the MoO4 tetrahedral units. Further, it is inferred from the nature of the Raman bands in the amorphized material that the Mo-O bond
lengths and bond angles have a range of values, instead of a few set values. The results of the present study as well as previous
high pressure-high temperature quenching experiments strongly support that pressure-induced amorphization in GMO is a consequence
of the kinetically impededβ toα phase transition. The system in frustration becomes disordered. The rare earth trimolybdates crystallizing in theβ′ structure are all expected to undergo similar pressure-induced amorphization. 相似文献
55.
56.
In situ angle dispersive synchrotron X-ray diffraction and Raman scattering measurements under pressure are em- ployed to study the structural evolution of Cu4Bi4S9 nanoribbons, which are fabricated by using a facile solvothermal method. Both experiments show that a structural phase transition occurs near 14.5 GPa, and there is a pressure-induced re- versible amorphization at about 25.6 GPa. The electrical transport property of a single Cu4Bi4S9 nanoribbon under different pressures is also investigated. 相似文献
57.
Stanisław Urban Joanna Czub Roman Dąbrowski Albert Würflinger 《Phase Transitions》2013,86(4-5):331-342
Differential thermal analysis (DTA) method was applied to study the pressure–temperature phase diagrams for four members of the 4′-alkyl-4-isothiocyanato-biphenyl (nBT) homologous series (n?=?9–12). These compounds exhibit a smectic E polymorphism enriched by a smectic A phase for two longest members. Measurements were performed in the temperature range 25–110°C and the pressure range up to 165?MPa. For all substances studied the pressure-induced phases were established with one or two triple points in the examined pressure range. In addition, for the 11BT and the 12BT the phases existing under atmospheric pressure disappeared under relatively low pressures. The results are compared with recently studied smectogenic n-alkyl-cyanobiphenyl (nCB) compounds. 相似文献
58.
Abstract Neutron scattering experiments on the two-dimensional Heisenberg ferromagnets Cs2 CuF4 and K2CuF4 have been performed around 2 ~ 3 GPa over 1·4–15 K. At ambient pressure both the intralayer and the interlayer exchange interactions in these two compounds are ferromagnetic. At about 2 GPa, the interlayer exchange coupling in Cs2 CuF4 is found to change from ferromagnetic to antiferromagnetic, while the ferromagnetic intralayer exchange interaction is maintained. Contrary to Cs2CuF4, the ferromagnetism in K2Cuf4 is not destroyed by pressure up to 9 GPa, that was confirmed in the early study of the magnetic susceptibility measurements. 相似文献
59.
Abstract X-ray diffraction has been measured for crystalline silicon, crystalline germanium, amorphous silicon and amorphous germanium at temperatures down to 100 K and pressures up to 20 GPa using a diamond anvil cell and synchrotron radiation. The structural phase transitions, including amorphization, take place in the pressure-temperature range. It has been found that the structures after the phase transitions strongly depend on the path in the pressure-temperature diagram through which the system undergoes the phase transitions. For any of the aforementioned four materials, the high-pressure phase with the p-Sn structure is quenched during a release of pressure at 100 K, and transforms into an amorphous state when heated up to around 2 GPa. The path dependence of the states is discussed in relation to the pressure dependence of the heights of the energy barriers which have to be overcome when phase transitions occur. The effect of a structural disorder on the phase transition is also discussed by comparing the experimental results for the crystalline and amorphous materials. 相似文献
60.
High pressure structural behavior of Bi2Fe4O9 has been studied by in situ angular-dispersive X-ray diffraction (ADXD) measurements up to 51.3 GPa. Two phase transitions have been observed at 7.6 and 22.6 GPa, respectively. A second high pressure structure (HP2) involving the tripling of lattice parameter c has been identified. An unusual amorphization occurs after releasing pressure. The high pressure phase transitions can be understood in terms of the increase in the coordination number of Fe3+ ion. The depressurization amorphization results from the appearance of the metastable HP2 and its collapse after releasing pressure. The results extend our understanding of pressure-induced amorphization. 相似文献