ELASTICITY AND STRUCTURE OF NA257FESI3O8 GLASS TO 14 GPA BY BRILLOUIN AND RAMAN SPECTROSCOPIES
We have carried out Brillouin and Raman spectroscopic studies on Na257FeSi3O8 glass (analog of aegirine crystal) with 95% enrichment of iron in the 57Fe isotope up to 12 and 14 GPa, respectively. In contrast to the compressive wave velocity (VP), the shear wave velocity (VS) anomalously decreases with pressure, reaching a minima at 2.3 GPa, and then increases. Density and the bulk, shear, and Young’s moduli and Poisson’s ratio for this glass as a function of pressure up to 12 GPa are presented. The best polynomial fit of the density versus pressure data yields: r = 2.71642 + 0.06202´P -0.00153´P2. The measured bulk modulus K and its pressure derivative are obtained as K = 41.5 ± 0.6 GPa, Ko¢ = 5.9 ± 0.2. Shear and Young’s moduli, and Poisson’s ratio show a marked modification around 2.3 GPa. These results are discussed in light of the structural changes inferred from the Raman data.