Light scattering apparatus for angular dependent studies of anisotropic materials

2005

111

107

By scattering from a variety of acoustic phonons, a complete stiffness tensor has been determined for crystalline beta-HMX. The results are compared with recent experimental and theoretical determinations of the elastic constants and bulk modulus. Reasons for disagreement are discussed in terms of experimental limitations and anharmonic effects. The observed ordering of stiffness constants, C(11) (18.4 GPa), C(22) (14.4 GPa), and C(33) (12.4 GPa), is qualitatively associated with physical phenomena including cleavage planes, patterns in crystal growth, and molecular packing. This interpretation is further corroborated by the linear compressibilities plotted in three crystallographic planes. The Voigt-Reuss-Hill bulk and shear moduli were found to be 9.9 and 3.7 GPa, respectively. The elasticity of beta-HMX is also discussed in relation to proposed mechanisms for the initiation of detonation.

Section: Crystal Parametersmentioning

confidence: 99%

The elastic constants and related properties of β-HMX determined by Brillouin scattering

Stevens

2005

111

107

“…52 This instrument permits the incident light to rotate independently of the crystal and eliminates cutting the crystal to conform to a 90°scattering configuration. Cutting induces bulk and surface defects which introduce significant errors in phonon direction determination and creates significant widening of the Rayleigh line that obscures the inelastically scattered Brillouin lines.…”

Section: A Brillouin Scattering Apparatus and Measurementsmentioning

confidence: 99%

Quantitative measurement of guest–host interactions in supramolecular systems: A comparative Brillouin scattering study of the Dianin’s compound clathrand and two of its isostructural clathrates

Sandstedt

Michalski

2000

Self Cite

Single, isomorphous crystals of the guest-free clathrand of Dianin's compound and two of its clathrates containing two ethanols and a heptanol, respectively, have been studied by Brillouin scattering to obtain their complete elastic constant tensors. The values found for individual elastic constants are related to microscopic interactions of the guests and host cage using the clathrand as the reference. Direct correlation of the interference of the guest heptanol molecule with the hexamer hydrogen-bonded network of the host cage to reduced stiffness of this clathrate is demonstrated. In contrast, the ethanol-containing clathrate is demonstrated to have negligible interaction of the guests on the host cage hydrogen bonding. Additionally, the ethanol guests are shown to provide a buttressing effect that increases the stiffness of the guest-host system in specific directions. The results are shown to be consistent with previous thermal conductivity and solid state NMR studies on these systems. The results demonstrate the use of macroscopic elastic constants in understanding the nature of the microscopic interactions in supramolecular crystals.

“…A four-circle, Brillouin-scattering instrument 25 was used that allows rotation of the incident light beam and crystal independently so that a large number of phonons can be accurately sampled. Frequency shifts were resolved using a Burleigh Fabry-Perot interferometer operated in the triple-pass configuration.…”

Section: Methodsmentioning

confidence: 99%

The elastic constants and related properties of the energetic material cyclotrimethylene trinitramine (RDX) determined by Brillouin scattering

Haycraft

Stevens

2006

Haycraft, James J.; Stevens, Lewis L.; and Eckhardt, Craig J., "The elastic constants and related properties of the energetic material cyclotrimethylene trinitramine (RDX) determined by Brillouin scattering" (2006 The acoustic phonons of cyclotrimethylene trinitramine ͑RDX͒ have been studied using Brillouin scattering. The analysis of the acoustic-phonon velocities allowed determination of the complete stiffness tensor for this energetic material. The results are compared to other recent experimental and theoretical determinations of the RDX elastic constants, bulk moduli, and shear moduli. The observed ordering of elastic constants, C 11 Ͼ C 22 Ͼ C 33 , is qualitatively associated with a ͑001͒ cleavage plane and molecular packing. This interpretation is further corroborated by the linear compressibilities plotted in three crystallographic planes, and a comparison to recent theoretical and experimental hydrostatic compression studies on RDX. Finally, the elasticity of RDX is compared to a recently published report on the beta polymorph of cyclotetramethylene tetranitramine's elasticity, and is related to several proposed mechanisms for detonation initiation.