Viscoelastic Relaxation of Molten Phosphorus Pentoxide

We report the first ever dynamic light scattering study of the viscoelastic relaxation in anhydrous liquid P$_{2}$O$_{5}$. Properties of the time decay of the dynamic structure factor, including the average structural relaxation time and the stretching exponent, were obtained for temperatures from 850 \r{ }C to near the glass transition (T$_{g}$ = 419 \r{ }C) using photon correlation spectroscopy. Analysis indicates that P$_{2}$O$_{5}$ is a strong glassforming liquid but one which exhibits an abnormally non-exponential relaxation near T$_{g}$. The viscoelastic behavior of P$_{2}$O$_{5}$ is compared with that of its metaphosphate counterpart to demonstrate how changes in bond connectivity influence both fragility and levels of dynamic heterogeneity.