Network Dynamics and Species Exchange Processes in Aluminophosphate Glasses: An in situ High Temperature Magic Angle Spinning NMR View
Sebastian Wegner, Leo van Wüllen and Gregory Tricot
In this contribution, we present an in situ high temperature 27Al and 31P magic angle spinning (MAS) NMR study of binary and ternary phosphate glasses at temperatures above the glass transition temperature TG. For binary phosphate glasses, xK2O−(1 − x)P2O5 and ternary aluminophosphate glasses 30K2O−xAl2O3−(70 − x)P2O5 with 7 < x < 15 dynamic exchange processes between the various phosphate species (and aluminate species) present in the glasses could be identified in the temperature range between TG and the maximum achievable temperature Tmax of our high temperature MAS NMR setup, TG < T < Tmax. This observation indicates rapid P−O−P and P−O−Al bond formation and bond breaking in the (alumino)phosphate glasses. From a modeling of the temperature dependence of these exchange processes, the activation energy EA for the corresponding process could be determined. These local bond breaking and making processes are ultimately linked to the macroscopic viscous flow and may indeed form the basic microscopic local step of viscous flow.