High pressure densification of lithium silicate glasses

We have carried out neutron diffraction and Raman scattering measurements on the lithium disilicate glass densified by the application of high pressure. The density of the glass increased monotonically with applied pressures up to 6 GPa. A shift of the first sharp diffraction peak (FSDP) toward larger Q vectors was found in the total structure factor S(Q) of the neutron diffraction spectra. The Si–O bond length in an SiO4 tetrahedron elongated by about 0.001 nm after densification under 6 GPa, while the nearest O–O distance did not change. However, an increase in distribution of the O–O distance was found after the densification. A low energy shift of 1080 cm−1 band, which is assigned to Si–O stretching mode, was observed in Raman scattering spectra of the densified glasses. It is consistent with the increase of Si–O bond length. We deduced from these results that the densification is caused by an increase of packing density of SiO4 tetrahedron, which is accompanied by a distortion of the tetrahedron.