共查询到20条相似文献,搜索用时 15 毫秒
1.
Here, we present new diamond anvils with a spherical support designed for applications in diamond anvil cell (DAC) technique. The main feature of the anvils is the diamond crown of a spherical shape. The assembly of the spherical diamond fixed within a spherical support of a seat made of tungsten carbide or hard metals provides enhanced stability, simple alignment, and large optical and X-ray aperture that makes it very useful for broad applications in DAC technique, particularly for single crystal X-ray and powder neutron diffraction. The anvils were tested in various experiments conducted in a wide pressure–temperature range and showed a very good performance. 相似文献
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ABSTRACT To understand the practical effects of pressure-transmitting media (PTM) on neutron diffraction using Paris–Edinburgh presses, diffraction patterns of MgO were collected to approximately 20?GPa using PTMs of Pb, AgCl, 4:1 methanol–ethanol (ME) mixture with and without heating, N2, and Ar. Hydrostaticity in the sample chamber estimated from the MgO 220 peak width improves in the order of Pb, AgCl, Ar, ME mixture, N2, and the heated ME mixture. Unlike previous results using diamond anvil cells, the unheated ME mixture is superior to Ar even after freezing, probably due to the cup on the anvil face. Considering these results and the sizable coherent scattering of Ne, which would show good hydrostaticity, we conclude that the ME mixture (preferably the heated one) is the best PTM in neutron experiments up to 20?GPa, while Ar can be substituted when a sample is reactive to alcohols. 相似文献
4.
A couple of normalisation criteria have been proposed to assess liquid structure data over the past decade. In this paper,
a critical examination of these and other plausible criteria is made. Neutron diffraction data from liquid krypton measured
by Clayton and Heaton is used to study these criteria. It is shown that if the structure factorS (Q)=1+γ (Q) satisfies the Krogh-Moe relation, namely
whereQ is the wavevector transfer andρ
0 the mean atomic number density,S (Q) is properly normalised. Subjecting such data to the other criteria would reveal, however, the quality of data in so far
as systematic errors and/or termination errors are concerned. If the data is measured with reasonable accuracy to sufficiently
large values of the wavevector transfer all these criteria would assess the quality of the data to almost the same extent.
This is established in this paper by improving and extending the liquid krypton data by procedures similar to that of Kaplow,
Strong and Averbach and subjecting this revised data to the various criteria. It is concluded, thereby, that (i) one can study
the neutron diffraction data from liquids using any of the criteria mentioned in the paper to improve the quality of the data
and (ii) for normalisation purposes the simple relation {ie328-2} would suffice. 相似文献
5.
为使中子粉末衍射谱仪满足小样品研究需要,设计了一维椭圆聚焦镜系统并对参数进行了优化,同时对椭圆聚焦镜的相关参数做了较为详细讨论。采用椭圆解析计算和中子追迹程序McStas模拟两种方法,计算了椭圆聚焦镜参数对样品处中子注量率的影响,并以样品处中子注量率最大化为目标给出了优化参数,结果表明,在单色器(椭圆左焦点)到样品(椭圆右焦点)距离为2.7 m情况下,采用超镜因子为3、长度为25 cm的椭圆聚焦镜,其最佳位置为距离样品560 mm处、椭圆长半轴为1 350.016 mm,从而可以提高样品处注量率7倍。 相似文献
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S. M. Yusuf 《Pramana》2008,71(4):695-704
We have studied magnetic correlations in several oxide materials that belong to colossal magnetoresistive, naturally occurring
layered oxide showing low-dimensional magnetic ordering, solid oxide fuel cell interconnect materials, and magnetic nanoparticles
using neutron diffraction and neutron depolarization techniques. In this paper, an overview of some of these results is given.
相似文献
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Crystal structure and magnetic behaviour of FeCrP have been investigated using magnetization and neutron diffraction measurements.
FeCrP crystallizes in orthorhombic FeZrP type structure (Pnma space group,Z = 4) in which Cr atoms occupy the pyramidal site and Fe atoms occupy the tetrahedral site with total preference. Structural
parameters including positional parameters have been refined. The refined values of positional parameters for Fe and Cr are
quite different from those in FeZrP. The nature of magnetization-temperature curve is suggestive of antiferromagnetic nature
withT
N = 280 (±10) K. Preliminary analysis of neutron diffraction pattern at 13 K is indicative of a rather complicated magnetic
structure. 相似文献
10.
Kazuki Komatsu Stefan Klotz Satoshi Nakano Shinichi Machida Takanori Hattori Asami Sano-Furukawa 《高压研究》2020,40(1):184-193
ABSTRACTA new high pressure cell for neutron diffraction experiments using nano-polycrystalline anvils is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performance is illustrated by powder neutron diffraction patterns of ice VII to ~82?GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of Fe3O4 at ambient conditions using this cell and discuss the current limitation and future developments. 相似文献
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Thomas F. Headen 《Molecular physics》2019,117(22):3329-3336
We present neutron diffraction data for liquid benzene measured as a function of temperature from 10°C to 70°C. Isotopic substitution and Empirical Potential Structure Refinement were used to obtain a complete spatial and orientational understanding of nearest neighbour correlations. We find an increased prevalence of nearest neighbour molecules where the angle between the aromatic planes is perpendicular, and at an angle of around 60°, when the temperature is reduced. There is no significant change in prevalence parallel stacked arrangements of nearest neighbour molecules as a function of temperature. The structure of the increased local order is consistent with structural motifs observed in benzene dimers and clusters from quantum chemistry calculations in the literature. 相似文献
13.
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.
相似文献
14.
In order to get the exact hydrogen-bonding scheme in triglycine sulphate (TGS), which is an important hydrogen bonded ferroelectric,
a single crystal neutron diffraction study was undertaken. The structure was refined to an R-factor of R[F
2] = 0.034. Earlier neutron structure of TGS was reported with a very limited data set and large standard deviations. The differences
between the present and the earlier reported neutron structure of TGS are discussed.
相似文献
15.
The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash
points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these
liquids at elevated temperatures through neutron diffraction. Here, the liquid consists of deuterated methanol and neutron
data was collected on the high-Q diffractometer at Dhruva, BARC. The corrected data at elevated temperatures (BP (boiling point) and double the BP) show that
there is a large change in the H-bonded structure of this liquid. The pre-peak or hump, known to be signature of H-bonded
clusters appears to be present at all the three temperatures studied. In the low-Q (scattering vector) data Ornstein-Zernike (OZ) behaviour is also observed. It is, however, seen that the intramolecular structure
does not change very much at higher temperatures. A detailed model analysis is in progress and would be reported later. 相似文献
16.
The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash
points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these
liquids at elevated temperatures through neutron diffraction. Here, the liquid consists of deuterated methanol and neutron
data was collected on the high-Q diffractometer at Dhruva, BARC. The corrected data at elevated temperatures (BP (boiling point) and double the BP) show that
there is a large change in the H-bonded structure of this liquid. The pre-peak or hump, known to be signature of H-bonded
clusters appears to be present at all the three temperatures studied. In the low-Q (scattering vector) data Ornstein Zernike (OZ) behaviour is also observed. It is, however, seen that the intramolecular structure
does not change very much at higher temperatures. A detailed model analysis is in progress and would be reported later. 相似文献
17.
We here report isotope substitution neutron diffraction experiments on two variants of high-density amorphous ice (HDA): its unannealed form prepared via pressure-induced amorphization of hexagonal ice at 77?K, and its expanded form prepared via decompression of very-high density amorphous ice at 140?K. The latter is about 17?K more stable thermally, so that it can be heated beyond its glass-to-liquid transition to the ultraviscous liquid form at ambient pressure. The structural origin for this large thermal difference and the possibility to reach the deeply supercooled liquid state has not yet been understood. Here we reveal that the origin for this difference is found in the intermediate range structure, beyond about 3.6 Å. The hydration shell markedly differs at about 6 Å. The local order, by contrast, including the first as well as the interstitial space between first and second shell is very similar for both. ‘eHDA’ that is decompressed to 0.20?GPa instead of 0.07?GPa is here revealed to be rather far away from well-relaxed eHDA. Instead it turns out to be roughly halfway between VHDA and eHDA – stressing the importance for decompressing VHDA to at least 0.10?GPa to make an eHDA sample of good quality. 相似文献
18.
An analysis of neutron diffraction data of liquid deuterated 1-propanol at room temperature to extract its molecular conformation
is presented. Being a big molecule with twelve atomic sites, the analysis is tricky and needs careful consideration. The resulting
molecular parameters are compared with electron diffraction (gas phase), X-ray diffraction (liquid phase) and MD simulation
results. Information about the hydrogen-bonded intermolecular structure in liquid is extracted and nature of the probable
molecular association suggested.
相似文献
19.
Abstract Neutron diffraction was until recently confined to pressures below ~ 3 GPa. This restricted range has limited the high-pressure structural information that is available for a wide range of phenomena for which neutron diffraction is the technique of choice. But now the recently-developed Paris-Edinburgh cell can achieve pressures up to ~ 30 GPa with a sample volume large enough to allow accurate structural studies with neutrons. After a period of development of the neutron scattering techniques needed to obtain the best possible results using the cell, a variety of successful structural studies have been performed. These illustrate the value of neutron diffraction in important areas such as locating hydrogen and other low-Z atoms in structures, the measurement of accurate structural pressure dependence and the examination of the changes in atomic thermal motion with pressure. 相似文献
20.
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