Micro-Raman
spectroscopy was used to determine the structural modifications
occurring in a simple ion-exchanged glass. The base lithium silicate
composition 30Li2O–70SiO2 was studied
as it underwent ion exchange, Li+ ↔ K+, at six temperatures spanning the glass transition point. Using
a well-developed relationship between the Si–O–Si bond
angle, the Si–O bond length, and Raman shifts, the reduction
in network molar volume and increase in compressive stress were estimated.
On the basis of the effect of the ion-exchange temperature, the existence
of a threshold energy below which the compressive stress manifests
as the reorientation of silica tetrahedra only and above which the
system relaxes by increasing the Si–O bond length is proposed.
Finally, the linear network dilation coefficient is revisited in terms
of these new data and an explanation given for its underestimation
and overestimation of stress at low and high temperatures, respectively.