Search

Spallation neutron and high-energy X-ray diffraction experiments are conducted to investigate the local structural changes in triphenyl phosphite (TPP) in the crystalline, glacial, glassy, and supercooled liquid phases. The results suggest that changes in molecular conformation and nearest-neighbor interactions are responsible for the existence of the glacial state.

The effects of high pressure (up to 9 GPa) on the thermal decomposition of ammonia borane, BH3NH3, were studied in situ by Raman spectroscopy in a diamond anvil cell. In contrast with the three-step decomposition at ambient pressure, thermolysis under pressure releases almost the entire hydrogen content of the molecule in two distinct steps. The residual of the first decomposition is polymeric aminoborane, (BH2NH2)x, which is also observed at ambient pressure. The residual after the second decomposition is unique to high pressure. Presumably it corresponds to a precursor to hexagonal BN where macromolecular fragments of planar hexagon layers formed by B and N atoms are terminated by H atoms. Increasing pressure increases the temperature of both decomposition steps. Due to the increased first decomposition temperature it becomes possible to observe a new high pressure, high temperature phase of BH3NH3 which may represent melting. [ABSTRACT FROM AUTHOR]

The vibrational density of states of amorphous beryllium hydride (a-BeH2) and lithium beryllium hydrides have been studied using inelastic neutron scattering, infrared, and Raman spectroscopies. The positions of the symmetrical (120–180 meV) and antisymmetrical (200–260 meV) Be–H stretching modes and those of the H–Be–H bending mode (50–120 meV) have been determined and the results discussed and compared with recent theoretical calculations. With the addition of lithium to the beryllium hydride network, the vibrational bands are shifted to lower energies, indicating a less rigid network. [ABSTRACT FROM AUTHOR]

High-pressure micro-Brillouin scattering is employed to investigate the pressure dependence of the sound velocity, refractive index, equation of state, and mechanical properties of amorphous BeH2. The refractive index n has been determined by using two scattering geometries (70° and 180°). The equation of state is deduced from the pressure dependences of the sound velocity. The bulk modulus is 14.2 (±3.0) GPa and its pressure derivative is 5.3 (±0.5). The polarizability is calculated from the refractive index and the density of the material. It increases with pressure while Poisson’s ratio decreases with pressure. [ABSTRACT FROM AUTHOR]

High-pressure micro-Brillouin scattering is employed to investigate the pressure dependence of the sound velocity, refractive index, equation of state, and mechanical properties of amorphous BeH2. The refractive index n has been determined by using two scattering geometries (70° and 180°). The equation of state is deduced from the pressure dependences of the sound velocity. The bulk modulus is 14.2 (±3.0) GPa and its pressure derivative is 5.3 (±0.5). The polarizability is calculated from the refractive index and the density of the material. It increases with pressure while Poisson’s ratio decreases with pressure. [ABSTRACT FROM AUTHOR]

The structure factors for amorphous BeD[sub 2] and BeH[sub 2] were measured using synchrotron x-ray and neutron diffraction techniques. The results show that the structure of amorphous BeD[sub 2] is comprised of corner-sharing tetrahedra and is therefore analogous to amorphous H[sub 2]O and BeF[sub 2]. A substantial increase in the height of the first sharp x-ray diffraction peak of BeD[sub 2] compared to BeH[sub 2] is interpreted as a marked increase in the extent of intermediate range order in BeD[sub 2] due to stronger network formation. A real-space comparison with liquid water, reveals that the structural isotopic quantum effects are quite different in the two hydrides. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]