Hiroshi Yamawaki

Distinct Responses to Mechanical Grinding and Hydrostatic Pressure in Luminescent Chromism of Tetrathiazolylthiophene

Luminescent mechanochromism has been intensively studied in the past few years. However, the difference in the anisotropic grinding and the isotropic compression is not clearly distinguished in many cases, in spite of the importance of this discrimination for the application of such mechanochromic materials. We now report the distinct luminescent responses of a new organic fluorophore, tetrathiazolylthiophene, to these stresses. The multichromism is achieved over the entire visible region using the single fluorophore. The different mechanisms of a blue shift by grinding crystals and of a red shift under hydrostatic pressure are fully investigated, which includes a high-pressure single-crystal X-ray diffraction analysis. The anisotropic and isotropic modes of mechanical loading suppress and enhance the excimer formation, respectively, in the 3D hydrogen-bond network.

HYDROGEN-BOND SYMMETRIZATION AND MOLECULAR DISSOCIATION IN HYDROGEN HALIDS

Abstract Hydrogen chloride is a simple diatomic molecule forming a planar zig-zag chain of molecules connected by hydrogen bonds in the solid phase. Raman spectra were measured for solid HCl to 60 GPa at room temperature. The molecular stretching frequency falls toward zero at about 51 GPa, where the molecular vibrational peaks disappear and the lattice peaks remain. The spectral changes are very similar to those observed for HBr at about 42 GPa and interpreted as hydrogen bond symmetrization. Molecular dissociation into diatomic halogen molecules, which has been observed for HBr, does not occur in HCl.

Crystal structure of anhydrous 5-aminotetrazole and its high-pressure behavior

Anhydrous 5-aminotetrazole (5-amino-1H-tetrazole, 5-ATZ) is an energetic material that produces a large amount of nitrogen gas by thermal decomposition and is often used as a gas generator agent. Although it is used widely as an air bag inflator, its crystal structure has not been determined yet. Thus, we performed a powder X-ray diffraction experiment, a Rietveld analysis, and the density functional theory calculation to investigate its structure and determined it to be an orthorhombic P212121 with a 1H-form molecule. We also investigated the high-pressure behavior and found that the orthorhombic phase is stable up to at least 11.6 GPa. Furthermore, the quantum molecular dynamics calculations at high-temperature and high-pressure of 5-ATZ were carried out and predicted the phase change including molecular decomposition.

Incommensurate Structure of Phosphorus Phase IV

There are six known phases for phosphorus at room temperature under high pressure. Only the structure of phase IV, which exists from 107 GPa to 137 GPa, remains unsolved. We performed a powder x-ray diffraction experiment and a Rietveld analysis and successfully determined its structure to be an incommensurately modulated structure by only 1 site of atomic position. High-pressure phases of halogens and chalcogens have previously been shown to have a similar modulated structure; however, phosphorus phase IV is different from them and was shown to be the third case.

Hexaaquairon(II) dipicrate dihydrate.

In the crystal structure of the title compound, [Fe(H(2)O)(6)](C(6)H(2)N(3)O(7))(2).2H(2)O, the centrosymmetric cationic iron complexes and picrate anions form separate stacks extending along the b axis. No picrate species ligate to the metal cation. Picrate ions are linked to one another in the stack via short intermolecular C.C contacts of 3.083 (4) and 3.055 (4) A. Variable-temperature X-ray diffraction measurements performed between room temperature and 93 K showed a linear decrease of the lattice parameters, suggesting that there is no phase transition.

Chemical Reactions and Other Behaviors of High Energetic Materials under Static Ultrahigh Pressures

We have studied behaviors of one of high sensitive explosives, RDX (hexahydro-1,3,5trinitro-1,3,5-triazine), under static ultrahigh pressures (up to 65 GPa) generated by using diamond anvil cells (DACs) using FT-IR spectroscopy and UV-VIS absorption spectroscopy. RDX changed its color into dark red when compressed up to 20 GPa with cesium iodide (CsI), filled as a pressure medium, but not when compressed RDX alone nor with potassium bromide (KBr). When RDX was compressed with CsI, intensities of characteristic IR absorption peaks of RDX decreased as the pressure increased, and did not returned to the intensities measured at ambient pressure, after the pressure was unloaded. On the other hand, when RDX was compressed alone, its color changed into yellow at pressures above 60 GPa. UV-VIS absorption spectra of RDX were also measured. The absorption peak shifted to 410 nm at 65.5 GPa from 243.5 nm at ambient pressure. It is assumed that the HOMO-LUMO band gap of RDX decreases with increasing the pressure. Introduction Chemical reactions can be triggered by mechanical forces in solids because solids support shear strains. When covalent bonds are bent, the energies of their highest occupied molecular orbitals (HOMOs) are raised, whereas the energies of their lowest unoccupied molecular orbitals (LUMOs) are lowered [1]. Thus, the gap between these levels, which determines a bond’s stability, is decreased [2]. When mechanical forces are applied to materials, the electronic structures of the materials will change, so that structural transformations or chemical reactions can proceed Materials Science Forum Online: 2004-09-15 ISSN: 1662-9752, Vols. 465-466, pp 189-194 doi:10.4028/www.scientific.net/MSF.465-466.189

Formation of large carbon cluster ions at graphite (HOPG) surfaces by laser irradiation

The formation process of carbon cluster ions by the irradiation of CO2 laser and N2 laser on the different surfaces of graphite (HOPG) has been investigated. Large cluster ions Cn+ (44 ≤ n ≳ 160) were observed by the first irradiation of CO2 laser pulse on a cut surface of which normal axis is perpendicular to the c-axis of the graphite, whereas only small cluster ions were obtained by the irradiation on cleaved surfaces. The N2 laser produced only small cluster ions on the cut and cleaved surfaces. The formation mechanism of the large cluster ions is considered to be the condensation of carbon vapor in gaps between graphite crystallites being exposed at the cut surface.

Phase Transition of a Structure II Cubic Clathrate Hydrate to a Tetragonal Form

The crystal structure and phase transition of cubic structure II (sII) binary clathrate hydrates of methane (CH4 ) and propanol are reported from powder X-ray diffraction measurements. The deformation of host water cages at the cubic-tetragonal phase transition of 2-propanol+CH4 hydrate, but not 1-propanol+CH4 hydrate, was observed below about 110 K. It is shown that the deformation of the host water cages of 2-propanol+CH4 hydrate can be explained by the restriction of the motion of 2-propanol within the 5(12) 6(4) host water cages. This result provides a low-temperature structure due to a temperature-induced symmetry-lowering transition of clathrate hydrate. This is the first example of a cubic structure of the common clathrate hydrate families at a fixed composition.

High-pressure powder x-ray diffraction experiments on Zn at low temperature

High-pressure powder x-ray diffraction experiments have been performed on Zn with a He-pressure medium at low temperature. When the sample was compressed in the He medium at low temperature, large nonhydrostaticity developed, yielding erroneous lattice parameters. On the other hand, when the pressure was changed at high temperatures, good hydrostaticity was maintained. No anomaly in the volume dependence of the c/a axial ratio has been found.

High-pressure spectroscopic measurement on diffusion with a diamond-anvil cell

We report a diamond-anvil-cell (DAC) technique developed for spectroscopic measurement on the diffusion process in molecular solids at high pressure. The diffusion processes of atoms, molecules, or their ionic species are investigated for a bilayer specimen by measuring the variation of infrared vibrational spectra with time. The experimental procedures for the protonic and molecular diffusion measurements on ice at 400 K and 10.2 GPa are presented as an example study. The in situ spectroscopic technique with a DAC significantly extends the pressure range accessible for diffusion measurement. The diffusion process at a rate of 10−16–10−14 m2/s can currently be observed at temperatures of 300–600 K and pressures up to several tens of gigaPascals.