Mechanical Structural Investigation of Ion-Exchanged Lithium Silicate Glass using Micro-Raman Spectroscopy

Micro-Raman spectroscopy was used to determine the structural modifications occurring in a simple ion-exchanged glass. The base lithium silicate composition 30Li(2)O-70SiO(2) 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.