Viscoelastic relaxation in molten phosphorus pentoxide using photon correlation spectroscopy

Abstract

A study of the viscoelastic relaxation in anhydrous liquid ${\mathrm{P}}_{2}{\mathrm{O}}_{5}$ is reported. 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 $850\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ to near the glass transition $({T}_{g}=419\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ using photon correlation spectroscopy. Analysis indicates that ${\mathrm{P}}_{2}{\mathrm{O}}_{5}$ is a strong glass-forming liquid but one that exhibits an abnormally nonexponential relaxation near ${T}_{g}$. The viscoelastic behavior of ${\mathrm{P}}_{2}{\mathrm{O}}_{5}$ is compared with that of its alkali-metal-modified metaphosphate counterparts $\mathrm{Na}\mathrm{P}{\mathrm{O}}_{3}$ and $\mathrm{Li}\mathrm{P}{\mathrm{O}}_{3}$, as well as with the mechanical relaxation of chalcogenide glasses, to demonstrate common patterns in dynamical behavior presumably arising from changes in the average connectivity of the glass structure.