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排序方式: 共有623条查询结果,搜索用时 218 毫秒
191.
Daisuke Yamazaki Eiji Ito Yoshinori Tange Takashi Yoshino Shuangmeng Zhai Hiroshi Fukui Anton Shatskiy Tomoo Katsura Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2007,34(4):269-273
In situ X-ray observations of the phase transition from ilmenite to perovskite structure in MnGeO3 were carried out in a Kawai-type high-pressure apparatus interfaced with synchrotron radiation. The phase boundary between
the ilmenite and perovskite structures in the temperature range of 700–1,400°C was determined to be P (GPa) = 16.5(±0.6) − 0.0034(±0.0006)T (°C) based on Anderson’s gold pressure scale. The Clapeyron slope, dP/dT, determined in this study is consistent with that for the transition boundary between the ilmenite and the perovskite structure
in MgSiO3. 相似文献
192.
Martín Crdenas-Soto Francisco J. Chvez-García 《Soil Dynamics and Earthquake Engineering》2007,27(5):475-486
We analysed in detail three earthquakes recorded in a small-aperture accelerometric array in Mexico City, using the correlation of the records as a function of time along the accelerogram and frequency. Ground response is strongly conditioned by the fundamental period of the soft soils at the site of the array (T0). Energy at periods longer than 2T0 is guided by the crustal structure (with a thickness of 45 km). The wave field at periods between T0 and 2T0 also consists of surface waves but guided by the upper 2–3 km of volcanic sediments in central Mexico. For periods smaller than T0, ground motion is uncorrelated among the stations. Our results indicate that seismic response of Mexico City, including its very long duration, results from deeply guided surface waves (between 2 and 45 km depth) interacting with the very local response of the soft surficial clay layer. 相似文献
193.
Thermal expansion has been measured by laboratory and synchrotron X-ray powder diffraction for end-member åkermanite (ak, Ca2MgSi2O7) and gehlenite (ge, Ca2Al2SiO7) in the range 20–1,500 K. In ak in the range 340–390 K, there is a negative linear thermal expansion in [001] direction. This is related to the phase transition from an incommensurate modulated structure (IC) to a normal one (N). The volumetric mean thermal expansion coefficients for ak and ge, obtained with a linear fit of the experimental data in the temperature range 298–1,400 K, are respectively 32.1×10–6 and 28.3×10–6 K–1 . The variation of the c/a ratio with temperature, due to different thermal expansion along the crystallographic axes, can be related to the different behaviour of the tetrahedral layers in the N and IC phases. Analysis of the variation of the superstructure peaks intensity across the phase transition confirms the tricritical behaviour of the IC/N transition in ak. 相似文献
194.
Danièle Valdes Jean-Paul Dupont Nicolas Massei Benoît Laignel Joël Rodet 《Comptes Rendus Geoscience》2005,337(15):1365-1374
In karst systems, rain events often result in a decrease of the conductivity (a tracer of dissolved phase transport) and an increase in turbidity (a tracer of suspended solids transport) at wells and springs. This study shows that the comparison of suspended solids and solute transport by the coupled approach of curves (Turbidity–Conductivity) and autocorrelations gives evidence of the transport processes in the karst network and allows understanding the karst hydrodynamics. To cite this article: D. Valdes et al., C. R. Geoscience 337 (2005). 相似文献
195.
Shigehiko Tateno Kei Hirose Nagayoshi Sata Yasuo Ohishi 《Physics and Chemistry of Minerals》2006,32(10):721-725
The stability and high-pressure behavior of perovskite structure in MnGeO3 and CdGeO3 were examined on the basis of in situ synchrotron X-ray diffraction measurements at high pressure and temperature in a laser-heated diamond-anvil cell. Results demonstrate that the structural distortion of orthorhombic MnGeO3 perovskite is enhanced with increasing pressure and it undergoes phase transition to a CaIrO3-type post-perovskite structure above 60 GPa at 1,800 K. A molar volume of the post-perovskite phase is smaller by 1.6% than that of perovskite at equivalent pressure. In contrast, the structure of CdGeO3 perovskite becomes less distorted from the ideal cubic perovskite structure with increasing pressure, and it is stable even at 110 GPa and 2,000 K. These results suggest that the phase transition to post-perovskite is induced by a large distortion of perovskite structure with increasing pressure. 相似文献
196.
A. R. Chakhmouradian K. Ross R. H. Mitchell I. Swainson 《Physics and Chemistry of Minerals》2001,28(4):277-284
A series of fluoride perovskites related to neighborite was investigated using X-ray and neutron diffraction techniques, and Rietveld profile refinement of powder diffraction data. The series (Na1? x K x )MgF3 comprises orthorhombic (Pbnm, a?≈? , b?≈? , c?≈?2a p , Z=4) perovskites in the compositional range 0?≤?x?≤?0.30, tetragonal perovkites (P4/mbm, a?≈? , c?≈?a p , Z=2) in the range 0.40?≤?x?≤?0.46, and cubic phases (Pm3¯m, Z=1) for x?>?0.50. The structure of the orthorhombic neighborite is derived from the perovskite aristotype by rotation of MgF6 octahedra about the [110] and [001] axes of the cubic subcell. The degree of rotation, measured as a composite tilt Φ about the triad axis, varies from 18.2° at x=0 to 11.2° at x=0.30 (as determined from the fractional atomic coordinates). Orthorhombic neighborite also shows a significant displacement of Na and K from the “ideal” position (≤0.25?Å). The tetragonal members of the neighborite series exhibit only in-phase tilting about the [001] axis of the cubic subcell (φ) ranging from 4.5° to 4.8° (determined from the atomic coordinates). The solid solution (Na1? x K x )MgF3, shows a regular variation of unit-cell dimensions with composition from 3.8347?Å for the end-member NaMgF3 (reduced to pseudocubic subcell, a p ) to 3.9897?Å for KMgF3. This variation is accompanied by increasing volumes of the A-site polyhedra, whereas the volume of MgF6 octahedra initially decreases (up to x=0.40), and then increases concomitantly with K content. The polyhedral volume ratio, V A /V B , gradually increases towards the tetragonal structural range, in agreement with diminishing octahedral rotation in the structure. The P4/mbm-type neighborite has an “anomalous” polyhedral volume ratio (ca. 5.04) owing to the critical compression of MgF6 polyhedra. 相似文献
197.
利用电磁波在导电媒质界面反射系数的附加相角,导出了电场垂直于入射面的非均匀电磁波在导电介质界面的类全反射横向偏移,并对横向偏移进行了相关计算,绘出了横向偏移随入射角的变化曲线. 结果表明:入射角在相移常数临界角、衰减常数临界角和90°处,横向偏移曲线存在三个间断点. 当入射角等于这三个角时,横向偏移为无穷大,即电磁波将沿界面传播;当入射角在这三个角附近时,横向偏移变得非常大. 相似文献
198.
斜压模,正压模和异常海温时间变化的位相关系 总被引:5,自引:2,他引:3
利用1958-1997共40年NECP/NCAR再分析大气资料和GISST海表温度资料集,研究了大气斜压模、正压模与海表温度变化这三者之间位相关系,并从大气动力学方程组解释了这些位相关系。指出:大气了斜压西风异常时间变化的位相落略微后于SSTA的变化位相,而正压西风异常的变化位相超前于SS-TA变化位相。斜压纬向风异常的变化又超前于正压异常纬向风的变化。斜压纬向风异常与海表温度异常之间存在正相关关 相似文献
199.
S. Ono E. Ito T. Katsura A. Yoneda M. J. Walter S. Urakawa W. Utsumi K. Funakoshi 《Physics and Chemistry of Minerals》2000,27(9):618-622
In situ synchrotron X-ray experiments in the system SnO2 were made at pressures of 4–29 GPa and temperatures of 300–1400 K using sintered diamond anvils in a 6–8 type high-pressure
apparatus. Orthorhombic phase (α-PbO2 structure) underwent a transition to a cubic phase (Pa3ˉ structure) at 18 GPa. This transition was observed at significantly lower pressures in DAC experiments. We obtained the
isothermal bulk modulus of cubic phase K
0 = 252(28) GPa and its pressure derivative K
′=3.5(2.2). The thermal expansion coefficient of cubic phase at 25 GPa up to 1300 K was determined from interpolation of the
P-V-T data obtained, and is 1.7(±0.7) × 10−5 K−1 at 25 GPa.
Received: 7 December 1999 / Accepted: 27 April 2000 相似文献
200.
K. Kuroda T. Irifune T. Inoue N. Nishiyama M. Miyashita K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2000,27(8):523-532
Determination of the phase boundary between ilmenite and perovskite structures in MgSiO3 has been made at pressures between 18 and 24 GPa and temperatures up to 2000 °C by in situ X-ray diffraction measurements
using synchrotron radiation and quench experiments. It was difficult to precisely define the phase boundary by the present
in situ X-ray observations, because the grain growth of ilmenite hindered the estimation of relative abundances of these phases.
Moreover, the slow reaction kinetics between these two phases made it difficult to determine the phase boundary by changing
pressure and temperature conditions during in situ X-ray diffraction measurements. Nevertheless, the phase boundary was well
constrained by quench method with a pressure calibration based on the spinel-postspinel boundary of Mg2SiO4 determined by in situ X-ray experiments. This yielded the ilmenite-perovskite phase boundary of P (GPa) = 25.0 (±0.2) – 0.003
T (°C) for a temperature range of 1200–1800 °C, which is generally consistent with the results of the present in situ X-ray
diffraction measurements within the uncertainty of ∼±0.5 GPa. The phase boundary thus determined between ilmenite and perovskite
phases in MgSiO3 is slightly (∼0.5 GPa) lower than that of the spinel-postspinel transformation in Mg2SiO4.
Received: 19 May 1999 / Accepted: 21 March 2000 相似文献