Refractive index of CaAl2Si2O8 glass and crystalline anorthite at pressures up to 5.0 GPa

Effect of pressure on the refractive index and relative density of the CaO·Al2O3·6SiO2 glass

“…The pressure dependence of the relative density of the CaO Á Al 2 O 3 Á 6SiO 2 glass exhibits a nonlinear behavior similar to the earlier obtained change in this property for other silicate glasses [34][35][36][37][38], in particular, for the CaAl 2 Si 4 O 12 glass shown in Fig. 1.…”

“…Polymorphic transformation of crystalline anorthite on the plot (d À d 0 )/d against P appears as a curve bend in the range of 2.6-2.9 GPa with a further decrease in the pressure coefficient of compressibility. A peculiar behavior of the plot (d À d 0 )/d against P in the pressure range of 2.0-4.0 GPa for anorthite glass and convergence of values of pressure coefficient of compressibility (d À d 0 )/dP for crystalline and glassy anorthite in the pressure range higher than phase transformation [33] support the similarity of structures of high-pressure crystalline anorthite and CaAl 2 Si 2 O 8 glass at high-pressure. This suggests that glasses under study in the pressure range of 2.0-6.0 GPa undergo structural changes of topologic character rather than those related to the changes in the coordination number of network formers.…”

“…Fig. 1 shows the pressure-induced change in the relative density of CaAl 2 Si 6 O 16 glass together with the data for previously studied CaAl 2 Si 2 O 8 [33] and CaAl 2 Si 4 O 12 [34] glasses.…”

“…1), particularly anorthite glass, suggests structural changes. Kuryaeva et al [33] compare pressure dependencies of changes in the relative density of anorthite glass and its crystalline analog. The comparison showed many common features in the pressure-induced behavior of CaAl 2 Si 2 O 8 and anorthite glass.…”

“…In this paper, a new results concerning the pressure-dependent behavior of refractive index for a CaO Á Al 2 O 3 Á 6SiO 2 glass containing equal mole fractions of Al 2 O 3 and CaO (12.5 mol% each) are reported. The obtained data are compared with those for CaO Á Al 2 O 3 Á 2SiO 2 [33] and CaO Á Al 2 O 3 Á 4SiO 2 [34] glasses also containing identical amounts of Al 2 O 3 and CaO (25.0 and 16.7 mol%, respectively).…”