In situ high-temperature crystallographic evolution of a nonstoichiometric Li2O·2SiO2 glass.

In this work, the high-temperature crystallographic evolution of crystalline phases in a complex lithium disilicate glass was investigated using synchrotron X-ray powder diffraction. The lattice parameters and unit cell volume of Li2SiO3 (LS), Li2Si2O5 (LS2), Li3PO4 (LP), and ZrO2 as a function of temperature were determined upon heating. It is found that the lattice parameter c of LS2 shows a "V"-shaped trend during heating. The crystallographic evolution of the LS2 phase has a close correlation with the LS phase, indicating the mutual interaction between LS and LS2 phases along the c axis during the nucleation/crystallization process. The phase evolution processes were different upon heating and cooling, and the unit cell volume of both LS and LP phases demonstrated different change rates. In this glass system, no LS2 was detected during cooling and the main phases formed during cooling process were LP, LS, β-cristobalite, and β-quartz. Interestingly, there were two forms of β-quartz with slightly different lattice constants, and the silica phases showed a near-zero expansion behavior. The crystallographic evolution mechanism is discussed.