Topology and glass structure evolution in (BaO)_x((B₂O₃)₃₂(SiO₂)₆₈)_{100 − x} ternary—Evidence of rigid, intermediate, and flexible phases

We examine variations in the glass transition temperature (T_g(x)), molar volume (V_m(x)), and Raman scattering of titled glasses as a function of modifier (BaO) content in the 25% < x < 48% range. Three distinct regimes of behavior are observed; at low x, 24% < x < 29% range, the modifier largely polymerizes the backbone, T_g(x) increase, features that we identify with the stressed-rigid elastic phase. At high x, 32% < x < 48% range, the modifier depolymerizes the network by creating non-bridging oxygen (NBO) atoms; in this regime T_g(x) decreases, and networks are viewed to be in the flexible elastic phase. In the narrow intermediate x regime, 29% < x < 32% range, T_g(x) shows a broad global maximum almost independent of x, and Raman mode scattering strengths and mode frequencies become relatively x-independent, V_m(x) show a global minimum, features that we associate with the isostatically rigid elastic phase, also called the intermediate phase. In this phase, medium range structures adapt as revealed by the count of Lagrangian bonding constraints and Raman mode scattering strengths.