Elastic phase diagrams of ternary Ge-P-S bulk glasses

Elastic phases of network glasses can be identified from a measurement of the non-reversing enthalpy ($\Delta $H$_{nr})$ near T$_{g}$ in T-modulated DSC. Glasses at low mean coordination number \textbf{\textit{r}} $<$ \textbf{\textit{r}}$_{c}$(1) possess a narrow $\Delta $H$_{nr}$(T) term that generally increases by an order of magnitude upon aging, which is characteristic of mechanically \textit{floppy phases}. Glasses in a \textbf{\textit{r}}$_{c}$(1) $<$\textbf{\textit{ r }}$<$ \textbf{\textit{r}}$_{c}$(2) range possess a $\Delta $H$_{nr}$ term that is minuscule and does not age, which is characteristic of \textit{intermediate} or \textit{self-organized phases }(IP)$.$ And glasses at high \textbf{\textit{r}} $>$ \textbf{\textit{r}}$_{c}$(2) possess a broad and asymmetric $\Delta $H$_{nr}$(T) term that ages, which is characteristic of \textit{stressed rigid phases}. Raman scattering and MDSC measurements on ternary Ge$_{x}$P$_{x}$S$_{1-2x}$ glasses have now been performed$^{1}$ and show \textbf{\textit{r}}$_{c}$(1) = 2.270 and \textbf{\textit{r}}$_{c}$(2) = 2.405, yielding an IP width ($\Delta $\textbf{\textit{r}}) of 0.135. Here \textbf{\textit{r}} = 2 +3x. In corresponding selenide glasses the IP width is found$^{2}$ at 0.210. The reduced width of the IP in sulfide glasses is attributed to S$_{8}$, P$_{4}$S$_{7}$ and P$_{4}$S$_{10}$ molecules demixing. By combining the present results with those on binary Ge-S and P-S glasses, elastic phase diagrams of ternary Ge-P-S glasses have now been constructed, and provide a global view of the three elastic phases. \newline 1. U. Vempati and P. Boolchand, J. Phys.: Cond. Matter, \textbf{16} S5121 (2004) \newline 2. S. Chakravarty et al. J. Phys.: Cond. Matter (in press) \newline Supported by NSF grant DMR 04-56472