Developments of nano-polycrystalline diamond anvil cells for neutron diffraction experiments

ABSTRACT

A 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.     

碳化硅压腔和高压下的中子衍射

使用宝石级碳化硅晶体作为压砧材料，成功研制出了碳化硅压腔（MAC），并应用全景式MAC进行了高压下物质的中子衍射实验研究。结果表明，MAC是一种既能产生高的压力又具有大的高压样品室的装置，特别适合于高压下的中子衍射研究。     

碳化硅压腔和高压下的中子衍射

使用宝石级碳化硅晶体作为压砧材料,成功研制出了碳化硅压腔（MAC）,并应用全景式MAC进行了高压下物质的中子衍射实验研究.结果表明,MAC是一种既能产生高的压力又具有大的高压样品室的装置,特别适合于高压下的中子衍射研究.     

New anvil designs in diamond-cells

New diamond anvils with conical support are introduced. Compared to conventional anvils the new design offers superior alignment stability, larger aperture, and reduced cost owing to significantly smaller anvil diameters. Except for table and culet, all surfaces are precision ground on a lathe, which lowers cost compared to faceted anvils. The conical design allows for steel supports, which are significantly easier and cheaper to manufacture than tungsten carbide supports. Conical support also prevents seat damage upon diamond failure. An additional new feature of the anvils is the roughened outer portion of the culet, which increases friction between the anvils and the gasket. This increases the height to diameter ratio of the pressure cell and prevents bonding between gasket and diamond, which causes ring cracks during pressure release. This technique replaces complicated diamond coating procedures. The anvils have been extensively tested for culets ranging from 0.1 to 1 mm diameter up to megabar pressures. A new anvil shape with cup-shaped culets to further increase the cell volume and gasket stability is also introduced.     

Diamond anvils with a spherical support designed for X-ray and neutron diffraction experiments in DAC

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.     

A nano-polycrystalline diamond anvil cell with bulk metallic glass cylinder for single-crystal neutron diffraction

ABSTRACT

A high-pressure cell for in-situ single-crystal neutron diffraction was developed. The cell uses nano-polycrystalline diamond anvils in a tubular load frame made of bulk metallic glass which is highly transparent to neutrons and does not produce Bragg reflections. Diffraction peaks from a sample can be measured from almost any direction and the simple geometry of the cell allows accurate attenuation corrections. We demonstrate the operation of the cell by ambient-pressure experiment using a single-crystal of NaCl on the D9 diffractometer at the Institute-Laue-Langevin. A high-pressure experiment was also carried out on a single crystal of ice VII at 2.35?GPa showing the potential to detect weak diffraction spots. The correct integration of weak reflections together with the simple attenuation correction will help to carry out precise structure analysis and address new scientific problems using neutron diffraction.     

The kiel/berlin pressure cells for neutron powder diffraction

Abstract

Two piston/cylinder type pressure cells for neutron powder diffraction are presented. They provide a large sample volume and hence allow rapid data collection at moderate flux neutron sources. Structure refinements from the diffraction data are possible. The maximum attainable pressure is above 2 GPa for Ti/Zr zero-scattering pressure cylinders. Both cells may be equipped with a micro-furnace. This allows measurement up to 700 K, simultaneously to the application of pressure. The low temperature setup for the cell-I is presented which will allow experiments down to 1·5K.     

Pulsed neutron powder diffraction at high pressure by a capacity-increased sapphire anvil cell

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.     

High pressure neutron diffraction studies using the Paris-Edinburgh cell

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.     

High pressure neutron diffraction using the paris-edinburgh cell: Experimental possibilities and future prospects

Abstract

High pressure neutron diffraction using the Paris-Edinburgh cell has attracted considerable interest ever since it has been shown that full structural data can be obtained at pressures up to 10 GPa. In this paper we will focus on the current state of this technique. Specifically, we report on new experimental possibilities concerning: i) access to “ultrahigh” pressures beyond 20 GPa, ii) experiments at variable temperatures down to 100 K, and iii) experiments on single crystals in inelastic neutron scattering. Current attempts to increase the pressure and temperature range are discussed.     

Compression of silver in a diamond anvil cell: Pressure dependences of strength and grain size from X-ray diffraction data

Two silver samples, coarse grained (c-Ag, grain size 300±30 nm) and nanocrystalline (n-Ag, grain size 55±6 nm), are compressed in a diamond anvil cell in separate experiments. The pressure is increased in steps of ∼3 GPa and the diffraction pattern recorded at each pressure. The grain size and compressive strength are determined from the analysis of the diffraction line-widths. The grain size of c-Ag decreases rapidly from 300±30 nm at ambient pressure to 40±8 nm at 15 GPa, and then gradually to 20±3 nm at 40 GPa. After pressure release to ambient condition, the grain size is 25±4 nm. The strength at ambient pressure is 0.18±0.05 GPa and increases to 1.0±0.3 GPa at 40 GPa. The grain size of n-Ag decreases from 55±6 nm at ambient pressure to 17±4 nm at 15 GPa and to 14±3 nm at 55 GPa. After release of pressure to ambient condition, the grain size is 50±7 nm. The strength increases from 0.51±0.07 GPa at ambient pressure to 3.5±0.4 GPa at 55 GPa. The strength is found to vary as the inverse of the square-root of the grain size. The results of the present measurements agree well with the grain-size dependence of strength derived from the hardness versus grain size data at ambient pressure available in the literature.     

Equation of state of 7LiD up to 6 GPa from neutron powder diffraction experiments

Abstract

The equation of state of ⁷LiD has been measured at 300 K up to 6GPa by 90° time-of-flight neutron scattering methods, in a novel cell with toroidal anvils. The increased precision over previous data allows to check theoretical calculations on lithium hydrides.

L'équation d'état de ⁷LiD a été établie à 300 K jusqu'à 6 GPa par des mesures de durée de vol de neutrons diffractés à 90°, dans une cellule à enclumes toroidales de conception originale. La prkision de ces mesures permet un test significatif des calculs théoriques sur les hydrures de lithium.     

Combined X-ray absorption and X-ray diffraction under high pressure

ABSTRACT

X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are two complementary structural techniques. Their combination improves the understanding of the effect of pressure on materials as illustrated by examples taken from studies on different types of materials (semiconductors, molecular solid, ferroelectric perovskite and gas mixture). The introduction of nanopolycrystalline diamonds anvils has extended XAS to high-energy edges with the possibility to use energy-scanning XAS beamlines where XRD can be performed in addition to XAS experiments.     

Diamond anvil cell, 50th birthday

The year 2008 marked the fiftieth birthday of the diamond anvil cell. Its birth took place when Alvin Van Valkenburg, while working with his colleagues, Charles E. Weir, Ellis R. Lippincott, and Elmer N. Bunting, first realized that he could look right through one of the diamond anvils and see a sample while it was at high pressure. In the following years, these scientists and many others adapted the diamond anvil cell to a wide variety of analytical techniques that have provided an impressive amount of information about materials at high pressures and high temperatures. But, virtually all of those techniques start with looking into the diamond anvil cell.     

Three-dimensional X-ray diffraction in the diamond anvil cell: application to stishovite

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.     

A new high P-T cell for neutron diffraction up to 7 GPa and 2000 K with measurement of temperature by neutron radiography

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.     

Structure refinement of sub-cubic-mm volume sample at high pressures by pulsed neutron powder diffraction: application to brucite in an opposed anvil cell

Neutron powder diffraction measurements of 0.9 mm³ of mixture of deuterated brucite and pressure medium were conducted at pressures to 2.8 GPa, using an opposed anvil cell and a medium-resolution diffractometer at Japan Proton Accelerator Research Complex pulsed neutron source. Spurious-free diffraction patterns were successfully obtained and refined to provide all structural parameters including Debye–Waller factors. Tilting of hydroxyl dipoles of brucite toward one of the three nearest-neighbor oxygen anions was confirmed to be substantial at pressure as low as 1.5 GPa. By this application, technical feasibility to analyze such a small sample has been newly established, which would be useful to extend the applications of neutron diffraction at high pressures.     

中子粉末衍射谱仪束流的椭圆聚焦镜设计

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。     

应用量子理论方法研究中子双缝衍射

通过严格求解薛定谔方程得到狭缝中的中子波函数,由基尔霍夫定律得到中子衍射波函数.最后得到中子双缝相对衍射强度与衍射图样位置之间的解析关系.计算所得结果与实验数据符合较好. 关键词： 中子衍射 薛定谔方程 基尔霍夫定律     

Magnetic correlations in oxides: Neutron diffraction and neutron depolarization study

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.