Slow homogenization of binary As-S melts and vibrational evidence of As Quasi-Tetrahedral Units in glasses.

FT-Raman profiling experiments on binary As-S melts are undertaken to establish the kinetics of homogenization of 1gram batch sizes using As$_{\mathrm{2}}$S$_{\mathrm{3}}$ and dry S as starting materials. These data reveal that melts take typically 3 weeks of reaction at 700\textdegree C to homogenize. Such slow kinetics of melt homogenization were noted earlier in Ge -- S binary and reflect the super-strong$^{\mathrm{1}}$ character (fragility index m \textless 20) of melts in the Intermediate Phase$^{\mathrm{1}}$ composition range. An important consequence of these homogenization experiments is that the Raman active 537 cm$^{\mathrm{-1}}$ mode predicted$^{\mathrm{2}}$ for the stretch vibration of S$=$As of Quasi Tetrahedral S$=$As(S$_{\mathrm{1/2}})_{\mathrm{3}}$ units is now observed in homogeneous glasses. Compositional trends of the mode scattering strengths, fragility index and the non -- reversing enthalpy of relaxation at T$_{\mathrm{g}}$ in these homogeneous glasses will be presented. \item S. Chakravarty, and P. Boolchand, J. Phys. Chem. B 118, 2249(2014). \item P. Chen et al. Phys. Rev. B 78, 224208 (2008).