Refractive index and compressibility of LiAlSi3O8 glass in the pressure range up to 6.0 GPa

The refractive index and the relative changes in the density for LiAlSi3O8 glass in the pressure range up to 6.0 GPa were obtained using a polarization-interference microscope and an apparatus with diamond anvils. The results were compared with the previous data for the NaAlSi3O8 and KAlSi3O8 glasses. The compressibility of glasses increases in a series of alkali metal cations Li+, Na+, K+. From the previously found dependence of the compressibility (at P=4.0 GPa) on the degree of depolymerization the value of NBO/T = 0.31 for LiAlSi3O8 glass was calculated. A high degree of depolymerization of the LiAlSi3O8 glass indicates not only a high content of NBOs atoms in the structural network, but also the presence of highly coordinated aluminum (according to the literature data similar to 9%). The proposed schematic reaction for the formation of different structural groups corresponds to the condition of the existence of 9% highly coordinated aluminum. (C) 2015 Elsevier Ltd. All rights reserved.