Yasuhiro Inamura

Structural studies of disordered materials using high-energy x-ray diffraction from ambient to extreme conditions

High-energy x-rays from a synchrotron radiation source allow us to obtain high-quality diffraction data for disordered materials from ambient to extreme conditions, which is necessary for revealing the detailed structures of glass, liquid and amorphous materials. We introduced high-energy x-ray diffraction beamlines and a dedicated diffractometer for glass, liquid and amorphous materials at SPring-8 and report the recent developments of ancillary equipment. Furthermore, the structures of liquid and amorphous materials determined from the high-energy x-ray diffraction data obtained at SPring-8 are discussed.

First Demonstration of Novel Method for Inelastic Neutron Scattering Measurement Utilizing Multiple Incident Energies

We succeeded in experimentally demonstrating that a series of two-dimensional maps of a dynamical structure factor in momentum–energy space with multiple incident energies can be simultaneously obt...

AMATERAS: A Cold-Neutron Disk Chopper Spectrometer

AMATERAS is a new disk-chopper-type spectrometer installed at Materials and Life Science Experimental Facility (MLF) of J-PARC. AMATERAS is equipped with an extra chopper for pulse shaping at the upstream position, in addition to a monochromating chopper, which conventional chopper spectrometers at pulsed source have. Owing to the use of these choppers and the high peak intensity from a coupled moderator source at MLF, the AMATERAS design realizes high-intensity and high-energy-resolution measurements in quasielastic and inelastic neutron scattering experiments. The spectrometer had the first neutron beam in May 2009. During the course of commissioning, the performance of the spectrometer was confirmed by conducting test experiments. AMATERAS is now open to users and is producing scientific outputs.

Intermediate range structure and low-energy dynamics of densified vitreous silica

Abstract The structure and low-energy dynamics of densified vitreous silica are studied with high accuracy by neutron scattering over a wide range of momenta and energy space. The structure factors (S(Q)) indicate that the change of the SiO4 tetrahedron (the short range order) by compaction is very small, but the intermediate range structure (IMRS) represented by the first sharp diffraction peak is strongly affected. This mainly attributed to a deformation of the sixfold ring structure. The low-energy dynamics the boson peak, BP also has a strong correlation with the change of IMRS. A reduction of the intensity of the boson peak by densification, however, cannot be explained by simple models such as phonon dumping or an eigenmode of IMRS. A shrinkage of the void space, surrounded by the sixfold ring structure, is related to the suppression of the low-energy dynamics. We consider that the origin of the boson peak can be attributed to a soft mode composed of an additional degree of freedom such as the void space.

Peculiar suppression of the specific heat and boson peak intensity of densified SiO2 glass

Abstract Low-energy dynamics of normal and densified vitreous silica was investigated by neutron scattering combined with the specific heat measurements. A large evolution of the Boson peak was clarified to be a suppression of the density of states at low energy, but not a peak shift as observed by Raman scattering. These results are inconsistent with a scenario based on a phonon scattering by a local density fluctuation, but consistent with soft potential model and a recent model by Nakayama.

INTERMEDIATE-RANGE STRUCTURE AND LOW-ENERGY DYNAMICS OF DENSIFIED SIO2 GLASS

Abstract The structure and dynamics of densified SiO 2 glasses have been studied by neutron scattering and Raman scattering as a function of the density. The detailed evolution of the intermediate-range structure, which appears as a change in the first and second diffraction peaks, were clearly observed and we found that a structural change has a linear proportionality to the density. The low-energy dynamics, the Boson peak, have also a strong correlation with the change of the intermediate-range structure. In this paper we discuss this correlation from the point of view that the six-fold ring structure has a key role.

Quasielastic neutron scattering studies on glass-forming ionic liquids with imidazolium cations

Relaxation processes for imidazolium-based ionic liquids (ILs) were investigated by means of an incoherent quasielastic neutron scattering technique. In order to clarify the cation and anion effects on the relaxation processes, ten samples were measured. For all of the samples, we found three relaxations at around 1 ps, 10 ps, and 100 ps-10 ns, each corresponding to the alkyl reorientation, the relaxation related to the imidazolium ring, and the ionic diffusion. The activation energy (Ea) for the alkyl relaxation is insensitive to both anion and alkyl chain lengths. On the other hand, for the imidazolium relaxation and the ionic diffusion processes, Ea increases as the anion size decreases but is almost independent of the alkyl chain length. This indicates that the ionic diffusion and imidazolium relaxation are governed by the Coulombic interaction between the core parts of the cations (imidazolium ring) and the anions. This is consistent with the fact that the imidazolium-based ILs have nanometer scale structures consisting of ionic and neutral (alkyl chain) domains. It is also found that there is a clear correlation between the ionic diffusion and viscosity, indicating that the ionic diffusion is mainly associated with the glass transition which is one of the characteristics of imidazolium-based ILs.

Hydration of alcohol clusters in 1-propanol-water mixture studied by quasielastic neutron scattering and an interpretation of anomalous excess partial molar volume

Quasielastic neutron scattering measurements have been made for 1-propanol-water mixtures in a range of alcohol concentration from 0.0 to 0.167 in mole fraction at 25 degrees C. Fraction alpha of water molecules hydrated to fractal surface of alcohol clusters in 1-propanol-water mixture was obtained as a function of alcohol concentration. Average hydration number N(ws) of 1-propanol molecule is derived from the value of alpha as a function of alcohol concentration. By extrapolating N(ws) to infinite dilution, we obtain values of 12-13 as hydration number of isolated 1-propanol molecule. A simple interpretation of structural origin of anomalous excess partial molar volume of water is proposed and as a result a simple equation for the excess partial molar volume is deduced in terms of alpha. Calculated values of the excess partial molar volumes of water and 1-propanol and the excess molar volume of the mixture are in good agreement with experimental values.

Neutron production from lead targets for 12-GeV protons

Abstract We carried out an experiment on neutron yields from typical cylindrical lead targets for 12-GeV protons by means of the Mn-bath moderation method. Our experimental results are, roughly speaking, consistent with those by Russian groups done for lower energy protons by different methods. The number of neutrons absorbed in the Mn-bath was determined to be 195 neutrons/proton, and the total neutron yield, including leakage neutrons, which were evaluated by calculations, was estimated to be 201 neutrons/proton for a 20cm (diameter) × 60cm (length) lead target. The total neutron yield as a function of the proton energy Ep, fitted to our data and the results of others, is expressed by the formula 2.0 + 29.2Ep 0.78, where Ep is expressed in GeV.

Dispersive excitation in different forms of SiO2

Abstract The dynamical structure factors of vitreous silica (v-SiO2), polycrystalline α-cristobalite and polycrystalline α-quartz are measured by inelastic neutron scattering. Clear dispersive behavior extending up to 55 meV is observed for all samples, irrespective of structural order. Especially, the similarity of dynamical behavior between v-SiO2 and polycrystalline α-cristobalite is found to be extremely remarkable in the range of E⩾7 meV. We consider that the essential difference between a glassy system and a crystalline one should be in the low-energy region below the Boson peak energy. The quantum excitation between a two-level system based on buckling motion may contribute to the anomalous low-energy excitation in glasses.