ELASTIC CONSTANTS OF ICE Ih, UP TO 2.8 KBAR, BY BRILLOUIN SPECTROSCOPY

The technique of high resolution Brillouin spectroscopy has been used to determine accurately the hydrostatic pressure dependence of the elastic constants of ice Ih in the full pressure range of phase stability 0 2.8 kbar. The percentage changes in the adiabatic elastic constants c,,, cI2. cI3, cS3, c,, and bulk modulus, over the pressure range, are 3.0, 7.2, 8.4, 2.8, -1.5 and 5.6 percent per kbar respectively. Longitudinal and transverse velocities for polycrystalline ice aggregates are also determined over the pressure range. Introduction It has been demonstrated that the technique of high resolution Brillouin spectroscopy is very effective for determining the elastic properties of ice [I-51. In fact Brillouin scattering represents the first application of a single measurement technique to determine and very accurately compare the dynamic elastic constants in local homogeneous regions of ice samples representing four different environments of formation, namely, artificial ice frozen from distilled water, monocrystalline glacial ice, bubbly lake ice and sea ice [2,3]. It was found that local elastic constants of ice formed under different conditions are basically the same. Consequently the hypothesis of. sample-to-sample variation, in particular, on the basis of age [6] was not substantiated. See ref. 3 for a detailed review. A pressure dependence of the elastic constants of single crystals of ice Ih, in the pressure range 0 0.4 kbar was reported by Brockamp and Ruter [7] using the ultrasonic pulse transmission technique. Very recently a relatively complete pressure dependence of the average longitudinal and transverse velocities of aggregates of ice Ih (and other polymorphs of ice) was determined by Shaw [8] using the above technique. In the present work the technique of high resolution Brillouin spectroscopy has been used to determine accurately, and for the first time, the hydrostatic pressure dependence of the elastic constants of ice Ih in the full pressure range of phase stability (0 2.8 kbar). The temperature dependence of the elastic constants have also been determined in the temperature range -4OC to -35OC. Experimental Technique and Analysis Brillouin spectroscopy is a relatively new experimental technique whose development has paralleled that of the laser. Brillouin scattering of light is attributed to those inhomogeneities, or fluctuations, in the optical dielectric constant of the scattering medium that are associated with the propagation of Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987104