H. Kiefte

Pressure dependence of the elastic constants of ice Ih to 2.8 kbar by Brillouin spectroscopy

The adiabatic elastic constants of single crystals of ice Ih from the Mendenhall Glacier, and the longitudinal and transverse speeds of sound of polycrystalline ice aggregates, have been measured in the range 0–2.8 kbar at −35.5 °C by Brillouin spectroscopy. The ice was held in a 10 kbar optical cell that allowed the sample to be rotated under loads of up to 10 kbar about one axis from outside the cell. The elastic constants C11, C12, C13, C33, and C44, and the bulk modulus are quadratic in the pressure range 0–2.8 kbar.

Temperature dependence of the width of the Raman Q branch in liquids nitrogen and oxygen

Interferometric measurements have been made of the width of the Q branch in the Raman spectra of saturated liquids N2 and O2 over the complete range from the respective triple points (63.15 K,54.35 K) to within 1 K of the critical point (126.26 K,154.58 K) in each case. The temperature dependence is similar for both liquids in the region above the normal boiling points (77.36 K,90.19 K): Near the latter temperatures the widths are 2 to 3 GHz, and the dominating feature is a sharp increase in width (to about 20 GHz) as the critical points are approached. A similar but less pronounced increase was also observed near the triple point in liquid O2. In the case of liquid N2, however, the linewidth remained approximately constant in the region below the normal boiling point.

Acoustic velocities and densities of polycrystalline ice Ih, II, III, V, and VI by Brillouin spectroscopy

The longitudinal and transverse speeds of sound of ice Ih, II, III, V, and VI have been measured by Brillouin spectroscopy in the range 0–10 kbar at −35.5 °C. The bulk adiabatic moduli derived from these measurements are 138.9, 98.7, 141.9, and 181.4 kbar for ice II, III, V, and VI, respectively, at pressures of 2.83, 2.76, 4.80, and 7.77 kbar, respectively. The isothermal compressions of the five phases have been measured directly by the contraction of a sample that was confined to a stainless‐steel tube.

Pure vibrational Raman spectra of simple liquids: O2, N2, CO, CH4, CF4

Interferometric techniques have been applied in a high resolution study of the polarized Raman components (Q branches) corresponding to the totally symmetric vibrational modes of CO, CH4, and CF4 in the liquid phase. Additional unpublished data for N2 and O2, as well as limited results of dilution studies in liquid argon, are reported. Emphasis is placed upon the measurement of variations in frequency shift and spectral width along the liquid–vapor coexistence line from the triple point to within 0.2 K of the critical point for each pure liquid. The character of the observed linewidth variations exhibits distinct differences from liquid to liquid, especially in the neighborhood of the triple and critical points. A consistent interpretation of the results suggests that a substantial contribution to the N2 and O2 linewidths is associated with the effect of intramolecular vibration–rotation coupling. The CH4 data support the predictions of Hills and Madden (i) that the long wavelength, hydrodynamic, density ...

Brillouin scattering studies of the SF6 crystal

The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants and the elasto‐optic coefficient ratios of oriented single crystals of SF6 at temperatures near the triple point. The values of the elastic constants at 221.0 K are C11 =34.1, C12=22.2, and C44=13.2 (in units of kbar) and the elasto‐optic coefficient ratios are P12 /P11 =0.92 and P44 /P11 =0.09. The temperature dependences of the elastic constants were determined and were found to be linear down to 187.0 K with ΔC11 /ΔT having a particularly large value of −0.46 kbar K−1 .

Cubic ice, snowflakes, and rare‐gas solids: Surface energy, entropy, and the stability of small crystals

Recent studies of the relation between the cubic and hexagonal forms of ice and of crystals of the rare gases show a common feature, in that, surface energy and entropy are important in determining the relative stability of crystal nuclei and of macroscopic crystals.

THE PRESSURE DEPENDENCE OF THE ELASTIC CONSTANTS OF ICE III AND ICE VI

The dependence of single-crystal Brillouin spectra on both crystal orientation and pressure (P) has been measured for phases III and VI of ice. The conditions, with P in kbar, were T=−20 °C, 2.2⩽P⩽3.0 for ice III, and T=−2 °C, 6.2⩽P⩽8.2 for ice VI. The pressure dependencies of the elastic constants and the polycrystalline elastic properties were determined.

Elastic characterization of a supported porous silicon layer by Brillouin scattering

Brillouin spectroscopy was used to study surface acoustic waves on a supported layer of (111)‐oriented porous silicon having a thickness of 2.7 μm and a porosity of 30%. The Rayleigh surface wave velocities were found to be significantly lower than corresponding velocities for crystalline silicon. A complete set of elastic constants for the porous layer was determined from the measured directional dependence of the surface wave velocity in the (111) plane. The best‐fit constants are C11=56.0±0.7 GPa, C12=6.7±0.3 GPa and C44=37.0±0.8 GPa. The anisotropy factor, η=1.50 indicates that the porous layer is elastically anisotropic.

High resolution Raman spectra of near‐critical CO2

The pure vibrational (Q branch) components of both the ν1 and 2ν2 Raman bands of supercritical CO2 have been studied using interferometric techniques. A significant broadening of the ν1 spectrum was observed as the critical point (Tc=304.15 K) was approached along the critical isochore.

On the solid–solid phase diagrams of Ar–O2 and Ar–N2 mixtures

The growth of large single crystals of Ar–O2 and Ar–N2 alloys is reported. The crystals were formed under near or quasiequilibrium conditions and it was found that minimum solute concentrations of about 4 1/2% (N2) and 5% (O2) were required in order to produce the hcp phase. Lower concentrations resulted in the fcc phase.