A neutron diffraction study of temperature-induced structural changes in potassium disilicate glass and melt

The structure of a potassium disilicate glass and melt has been investigated as a function of temperature using neutron diffraction. Temperature-induced structural changes resulting from the reequilibration of the system in the supercooled liquid state could be assessed on both the short and medium-range scales. A progressive disordering of the potassium environment is observed for increasing temperature, without any discontinuity through the glass transition. By contrast, changes in the silicate network occur only above the glass transition temperature in the supercooled liquid and liquid states, and affect mainly the medium-range order as demonstrated by the sharp increase of the intensity of the peak at low-Q values in the melt. These changes are interpreted on the basis of structural models provided by RMC simulations. A conformational relaxation of polymerised parts of the network forming the boundaries of potassium hosting cages is put in evidence and related to the particular dynamics of this melt.