Pressure-induced structural changes of basaltic glass

The structural determinations of basaltic glass under pressure were conducted. The obtained structure factor, S(Q) indicates that the position of the first sharp diffraction peak (FSDP) shifts to higher-Q region with increasing pressure up to 6 GPa. This result indicates the intermediate-range order structure of glass becomes compact. The radial distribution function, RDF shows the shrinkage of the average T-T length with increasing pressure, but indicates no detectable change of the average T-O length (T = Si(4+)and Al3+) and its coordination. This result implies that the positional shift of the FSDP is attributed to the polymerization of TO4 tetrahedra to form ...-T-O-T-... linkage, with the concomitant narrowing of the mean T-O-T angle. The RDF also shows that the distances of Fe(Mg)-O extend due to the changes in the structural roles of Fe and Mg from the network modifiers to the charge-balancing cations. The structural data of the recovered condition imply that the tetrahedral networks of the present glass is permanently polymerized and densified after compression. On the other hand, the network modifier cations undergo both contraction and relaxation processes.