共查询到18条相似文献,搜索用时 0 毫秒
1.
Takuo Okuchi Masashi Yoshida Yoshiki Ohno Naotaka Tomioka Narangoo Purevjav Toyotaka Osakabe 《高压研究》2013,33(4):777-786
A new design of opposed anvil cell for time-of-flight neutron powder diffraction was prepared for use at advanced pulsed sources. A couple of single-crystal sapphire sphere anvils and a gasket of fully hardened Ti–Zr null alloy were combined to compress 35 mm3 of sample volume to 1 GPa and 11 mm3 to 2 GPa of pressures, respectively. A very high-quality powder diffraction pattern was obtained at Japan Proton Accelerator Research Complex for a controversial high pressure phase of methane hydrate. The counting statistics, resolution, absolute accuracy and d-value range of the pattern were all improved to be best suitable for precise structure refinement. The sample is optically accessible to be measured by Raman and fluorescence spectroscopy during and after compression. The current cell will be an alternative choice to study hydrogenous materials of complex structures that are stable at the described pressure regime. 相似文献
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Abstract For phase transition studies, neutron powder diffraction offers a number of important advantages over x-ray based techniques, for example ab-initio structural determination. There are two distinct methods using either monochromatic angular dispersive geometry on a reactor cold source or time-of-flight energy-dispersive techniques requiring a pulsed neutron source. Both techniques offer comparable resolution but have differing advantages for high pressure studies. Recent studies illustrate the benefits of the two methods and the application of these to solve unknown crystal structures. 相似文献
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The structure of the aminoacid, Ls-threonine [NH 3 + CH(CHOHCH3)COO?], space groupP212121,a=13.630(5),b=7.753(1),c=5.162(2) Å,z=4, has been determined from neutron diffraction data using direct methods. The intensities of 1148 neutron Bragg reflections were measured from a single crystal. The structural parameters were refined by the method of least squares using anisotropic temperature factors. The finalR(F 2) is 0.068. The structure was also refined from the x-ray data of Shoemakeret al (1950J. Am. Chem. Soc. 72 2328); there is good agreement between the two sets of heavy atom parameters. The parameters of hydrogen atoms are of course more precisely determined in our neutron study. The molecular conformation and the hydrogen bonding scheme are discussed. Weighted average values of bond distances and angles from 14 aminoacid structures with ionized carboxylic groups studied by neutron diffraction at Brookheven and Trombay are also presented. 相似文献
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Structural behaviour of silver nitrate (AgNO3) at low temperatures has been investigated by neutron powder diffraction and differential scanning calorimetry (DSC). Analysis
showed abnormal changes in the rotations of nitrate (NO3) anions and thermal displacement parameters of the atoms near 220 K and 125 K. However, the basic lattice is compatible with
the orthorhombic symmetry (space group Pbca) till 12 K. The fine, small-scale structural anomalies probably originate from
freezing of reorientation of NO3 ions from high-temperature disordered phase.
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Abstract Using angle-dispersive diffraction techniques and synchrotron radiation, we have made a detailed re-examination of the high-pressure behaviour of a number of core II-VI, III-V and group IV semiconductors. Despite much previous work on these materials, the good resolution afforded by angle-dispersive techniques, and the high-sensitivity of the image-plate area detector have yielded many new results which reveal that the accepted structural systematics have to be modified quite substantially. In this paper, we summarise the newly emerging structural systematics, and use the results to show how access to full 2-d powder patterns has proved essential in determining correct crystal structures. 相似文献
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Yann Le Godec Martin T. Dove Simon A.T. Redfern Matthew G. Tucker William G. Marshall Gérard Syfosse 《高压研究》2013,33(5):263-280
Abstract This paper reports developments to enable neutron diffraction at simultaneous high temperatures and pressures using the Paris-Edinburgh cell. These include a new design of a cell assembly with internal heating. One of the novel features of our system is the use of neutron radiographic methods for measurement of temperature. Fully refinable neutron diffraction patterns obtained by time of flight technique with our apparatus are found to be of comparable quality to previous high-pressure studies at ambient temperatures. In this paper we describe the procedures for the generation and measurement of pressure and temperature and illustrate the quality of the data which can be obtained. The present system may be used on a routine basis for experiments up to 7 GPa and temperature approaching 2000 K. Current attempts are discussed for extending these measurements to a wider domain of pressures and temperatures. 相似文献
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Three-dimensional X-ray diffraction can be used for characterizing the orientation, position, and strain tensor of single grains in a polycrystalline aggregate. Here, we show how the method is well suited for diamond anvil cell data with heterogeneous grain sizes, with an application to two samples of stishovite at 15 and 26 GPa. For each grain, we obtain a well-defined orientation matrix and cell parameters. Center of mass position can also be adjusted to the experimental data, with errors in the present experiment. Finally, strain tensors are adjusted for the individual grains. The stress distribution obtained is in agreement with expectations from the diamond anvil cell geometry and previous measurements of stishovite strength. Advantages and potential for improvement of the method are then discussed. 相似文献
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V. P. Glazkov B. N. Savenko V. A. Somenkov D. V. Sheptyakov S. Sh. Shilstein 《高压研究》2013,33(3-6):201-207
Abstract The crystal structure of Nd2CuO4 has been studied by neutron diffraction at pressure up to 5 Gpa. The volume compressibility value was determined as 5·6·10?3/Gpa. The decrease of positional parameter of neodymium at high pressure has been observed. This structural change is explained by pressure induced neodymium ions charge increase. 相似文献
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The interplay between the lattice and magnetism in La(Fe11.4Al1.6)C0.02 studied by powder neutron diffraction 下载免费PDF全文
The crystallographic structure and magnetic properties of La(Fell.4Alz.6)C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe11.4Al1.6)C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites: FeI (8b) and FeII (96i), and that A1 atoms preferentially occupy the FeII site. A ferromagnetic state can he induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe11.4Al1.6)C0.02 has no net magnetization in the paramagnetic (T 〉 TN = 182 K) or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances. 相似文献
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The interplay between the lattice and magnetism in La(Fe<sub>11.4</sub>Al<sub>1.6</sub>)C<sub>0.02</sub> studied by powder neutron diffraction 下载免费PDF全文
The crystallographic structure and magnetic properties of La(Fe 11.4 Al 1.6 )C 0.02 are studied by magnetic measure- ment and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe 11.4 Al 1.6 )C 0.02 crystallizes into the cubic NaZn 13 -type with two different Fe sites: Fe I (8b) and Fe II (96i), and that Al atoms preferentially occupy the Fe II site. A ferromagnetic state can be induced at a medial temperature of 39 K–139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe 11.4 Al 1.6 )C 0.02 has no net magnetization in the paramagnetic (T > T N = 182 K) or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe–Fe bond length indicates that the ferromagnetic state prefers longer Fe–Fe distances. 相似文献
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《Solid State Ionics》2002,150(3-4):431-442
Dodecatungstophosphoric acid hexahydrate H3PW12O40·6H2O crystal structure has been investigated by neutron powder diffraction (NPD) at different temperatures in the 10–358 K range. A nonconvergent reversible phase transition has been noticed at about 320 K. This transition is associated with a change in dynamic equilibrium of hydrate species and partial reduction/oxidation (redox) W6+↔W5+. Expressive structure changes lie in the P---O bonding inside Keggin's anion and the H5O2+ conformational angle. 相似文献
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T. Radnai T. Megyes I. Bak T. Kosztolnyi G. Plinks H. Ohtaki 《Journal of Molecular Liquids》2004,110(1-3):123-132
New molecular dynamics simulations with optimised potentials for liquid simulation are presented for liquid formamide at high pressures and high temperatures. The structural results are compared to those found by X-ray diffraction measurements, and the H-bonding structure is analysed in detail. While it is ambiguous from purely experimental data, the simulation results support the idea that pressure increase can enhance ring dimer formation at the expense of linear chain structure, but increasing temperature results in an opposite effect. Dynamical results (reorientational correlation times and lifetimes of hydrogen bonds) are in agreement with these findings. 相似文献
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P. Ruello L. Desgranges G. Calvarin G. Petot-Ervas 《Journal of Physics and Chemistry of Solids》2005,66(5):823-831
X-ray and neutron powder diffraction studies of UO2 were performed under controlled oxygen partial pressure between room temperature and 1673 K. More than 40 neutron diffraction patterns were recorded. The thermal expansion coefficient of UO2 and the temperature dependence of Debye-Waller factors for oxygen and uranium atoms were determined. The dependence of Debye-Waller factors as a function of temperature is linear and the thermal expansion coefficient follows the classical Debye regime within the temperature range 300-1000 K. Above 1200 K, a departure from this quasi-harmonic behavior is clearly observed. Both an abnormal increase of the thermal expansion and of the oxygen sublattice disorder are evidenced. The departure of the lattice parameter from a linear thermal variation is found to be thermally activated with an effective activation energy close to 1 eV, very similar to the activation energy already found for the electrical conductivity. This new result suggests that polarons may affect the mean lattice parameter. A new thermodynamic model is then proposed to explain the heat capacity thermal variation by only three contributions: harmonic phonons, thermal expansion and polarons. 相似文献
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The temperature variation of the Debye-Waller factors of Cs+ and Cl− ions in CsCl powder has been studied using X-ray powder diffraction. A continuous flow cryostat has been used to record the
diffractograms and the integrated intensities of the Bragg peaks at different temperatures have been obtained. The integrated
intensities of the odd and even reflections have been analysed following the structure of the CsCl compound and the Debye-Waller
factors of the Cs+ and Cl− ions have been estimated. The results have been verified by structure factor least squares refinement. Theoretical shell
model lattice dynamical calculations have been done using a 7-parameter model in the harmonic approximation and the values
compared with the present X-ray measurements. 相似文献