Fundamental Materials Science

4B. From Structural to Mechanical Properties of Disordered Solids

Invited Talk

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P. Boolchand1,S. Ravindren1, K.Gunasekera1, S. Bhosle1, S.Chakraborty1, C.Holbrook1, P.Chen1 and R.Bhageria1
1 Department of Electrical and Computing systems,College of Engineering and Applied Science,University of Cincinnati,Cincinnati, OH 45221-0030

A key  feature  in observing topological phases of chalcogenide glasses is the recent recognition of delayed homogenization of their non-stoichiometric melts as observed in  As-Se(or S) and Ge-Se(or S) binary systems.  The recognition emerged FT-Raman profiling of typically 2 gram sized  melts performed in-situe as starting materials were reacted in evacuated quartz tubings over 7 days or more till the observed lineshapes taken along the length of tubes became identical. At that point melts were taken to be homogeneous with the stoichiometry variation less than 1/2%.  In these glasses of proven homogeneity, fragility index (m) measurements were performed using modulated DSC, and have shown global minima in m that are centered approximately in compositional windows where the isostatically rigid Intermediate Phase (IP) is observed. The minimum of the fragility index of approximately 15 in these glass systems, is suggestive of super-strong melts. Such melt compositions at the reaction temperature of the starting materials, possess viscosity that are at least 1 to 2 orders greater than those for compositions residing outside the IP. The hindered diffusion of such super-strong melt compositions serves to delay melt homogenization of non-stoichiometric batch compositions in general.

Once homogenized the Ge-Se(S) and As-S binary systems reveal reasonably sharp square-well like reversibility windows. On the other hand, in the case of the As-Se and P-Se binary systems, the enthalpy of relaxation at Tg near the rigidity transition (20 mole% of As or P)  is smeared. Remarkably, a eutectic occurs in both systems close to the rigidity transition, and apparently alters the aging behavior of such glass compositions due to segregation of glassy backbones.    

Keywords: Rigidity Theory, Raman scattering, Modulated DSC

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