Structure of LixRb1-xPO3 glasses near the glass transition

The temperature dependence of mixed alkali metaphosphate LixRb1-xPO3 (x = 1, 0.5, 0) structures has been studied from room temperature up to about 20 K above the glass transition temperature (Tg) by means of neutron diffraction and reverse Monte Carlo modelling. The results show that the structural changes are limited to a slight temperature-induced broadening of the peaks in S(Q) and a linear thermal expansion of 50-100 ppm K-1. Furthermore, the possible diffusion pathways of the mobile ions have been investigated by the bond valence technique and the results show that they are not significantly affected as the glass is brought above Tg. The decrease in activation energy that occurs above Tg is thus attributed to an increased coupling between the motions of the mobile ions and the relaxation of the phosphate network.