Structural differences between unannealed and expanded high-density amorphous ice based on isotope substitution neutron diffraction

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.     

Origin of low-frequency local vibrational modes in high density amorphous ice

Incoherent-inelastic neutron scattering data are obtained from 5-80 K for high-density amorphous (hda) ice in the region 0-135 cm(-1). An excess contribution to the vibrational density of states is identified near 20 cm(-1). The origin of these vibrations has been identified by lattice dynamics calculations on an "experimental" structure derived from reverse Monte Carlo analysis of hda ice neutron diffraction data. An interpretation that localized oscillations of short chains and isolated water molecules are responsible for the excess low-frequency modes is consistent with our data.     

A tof neutron diffraction system for high pressure and low temperature

Abstract

Time-of-flight method of neutron diffraction is applied for materials under high pressure and low temperature. Extra-scattering from the pressure cell is reduced by geometrical design and by shielding with boron-plastics. Temperature is controled by adjusting the supply of liquid nitrogen: Successive transformations with pressure are observed in heavy ice.     

Vibrational spectra of high- and low-density amorphous ice,ice Ic,and ice Ih by neutron scattering

Abstract

The vibrational spectra of high- and low-density amorphous ice made ice Ic and Ice Ih have been obtained at 15 K using inelastic incoherent neutron scattering     

Structural behaviour of AgNO3 at low temperatures by neutron diffraction

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.      

Reappraisal of the published neutron diffraction data on amorphous ferromagnetic alloys

A reanalysis of the previously reported neutron diffraction data on glassy ferromagnetic alloys suggest that the spin-wave energies of some glasses renormalize in accordance with the predictions of the itinerant-electron model. This observation is shown to have a direct bearing on the discrepancy between the spin-wave stiffness coefficient values D_s (neutron diffraction) and D_m (magnetization) found in certain amorphous ferromagnets.     

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.     

Energy deposition effects on amorphous selenium,by low temperature neutron irradiation

We have observed recently that neutron irradiation at low temperature can induce very strong changes in configurational disorder of glasses. This conclusion has been drawn from enthalpy change diagrams performed near Tg, by differential scanning calorimetry, on amorphous selenium. A progressive change was observed from a stabilized relaxation state to a highly quenched state as a function of the neutron dose. We explain these effects by a local heating process.

The irradiation was done at low temperature (30 K) and fission and capture effects were shielded by enclosing samples in NB cells.     

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。     

Investigations of texture formation in geomaterials by neutron diffraction with high pressure chambers

Abstract

This paper suggests a classification of texture in quartzitic rocks. Possible mechanisms of texture formation and their relation to tectonic processes are discussed.

A scheme for the experimental varification of some models describing the evolution of deformation structures in geological materials in dependence on various erxternal conditions (high pressures, temperatures, various loadings, etc.) acting on a sample is proposed.

To investigate “in situ” the mechanisms of texture formation in rocks, high pressure devices are under construction. They will be built of a special T_i ? Z_r alloy, which has zero coherent scattering lenght and therefore is well suited for neutron diffraction investigations. Two different devices are proposed. The first one allows neutron diffraction measurements of sample volumes up to 4 cm³, a hydrostatic pressure of 1, 5 GPa, a temperature of 300° C, and uniaxial compression up to 50 kN. Pressure temperature and axial load are measured inside the chamber. Besides during the experiment, diagrams of load, elastic wave velocities and acoustic emission will be recorded. The second chamber is designed to investigate the mechanisms of texture formation in polycrystal samples (rocks or their imitations) at temperatures up to 800° C and axial compression with a force of up to 150 kN.     

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.     

Thermodynamics of ice at high pressures and low temperatures

A new equation of state of ice Ih recently proposed by Feistel and Wagner [J. Phys. Chem. Ref. Data 35 (2006) 1021-1047] is used to study the phenomena related to the equilibrium isentropic compression of an ice-water mixture and dynamic loading of solid ice. New results are presented concerning the properties of the new equation of state, equilibrium solid-liquid phase transitions and Hugoniots of low-temperature (100 K) and temperate (263 K) shock-compressed ice.     

A search for anharmonic effects in NpO2 at low temperature by neutron diffraction

A single crystal neutron diffraction experiment has been performed on NpO₂ to search for anomalies in the Debye-Waller factors associated with the as yet unexplained 25 K phase transition. Data were collected out to a maximum momentum transfer of 16 Å⁻¹. A detailed analysis shows no significant changes of the thermal parameters when cooling below 25 K. This result effectively eliminates the most recent proposal that a dynamical distortion of the oxygen sublattice occurs.     

Structure determination of Ls-threonine by neutron diffraction

The structure of the aminoacid, L_s-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.     

Order in amorphous polystyrenes as revealed by electron diffraction and diffraction microscopy

Ordered regions ranging in size between 15 and 45 Å have been established in several atactic polystyrenes of various molecular weights (4800; 51,000; and 1,800,000) as well as in an amorphous isotactic polystyrene by means of electron diffraction and high-resolution diffraction microscopy. The order is due to long-chain polymer molecules which tend to align more-or-less parallel to one another with a constant average spacing. The orderly chain packing can be disturbed upon cross-linking by electron irradiation, the disturbance being manifested in the irreversible changes in the d spacing and broadening of one of the diffuse rings which is inter-molecular in origin. From the results obtained, the high-resolution diffraction microscopy technique appears to have the potential for resolving the question regarding the presence of order in unoriented amorphous polymers. The technique can also differentiate between a broadened diffuse ring due to small crystallites and another due to paracrystals containing numerous defects.