Vibrational study of thermally ion-exchanged sodium aluminoborosilicate glasses

• Ion-exchange induces local changes in glass structure below Tg.
• Detailed micro-Raman depth profiling of ion-exchanged glasses
• The induced structural rearrangements depend on the type of guest cation.
• Cation acidity is a key parameter affecting local structural rearrangements.

Thermally ion-exchanged M+-for-Na+ (M = K and Ag) aluminoborosilicate glasses were obtained from the glass (SiO2)60(B2O3)10(Al2O3)6(Na2O)20.2(ZrO2)3.7(Sb2O3)0.1 (in mol%) and studied by infrared reflectance and micro-Raman spectroscopy. The results of both techniques are consistent with local structural rearrangements induced by ion-exchange below glass transition temperature, Tg, and are expressed for the silicate network by the chemical equilibrium Q2 + Q4⇔2Q3 where Qn represents a silicate tetrahedron with n bridging oxygen atoms. Replacement of Na+ by K+ was found to shift this equilibrium to the right, while the introduction of Ag+ ions causes the opposite effect. Micro-Raman depth profiling showed that these structural changes occur within a layer whose thickness depends on the type of the guest cation and the conditions of ion-exchange; the thickness is about 50 μm for Ag+ ions exchanged at 340 °C for 180 min and about 40 μm for K+ exchanged at 325 °C for 6 h.