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New insights into the Glass Structure and Melt Dynamics of Ge-As-Se Alloys: Topological Phases, Eutectic Effects, Slow Homogenization of Melts and Nanoscale Phase Separation Effects

Ravindren, Sriram
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427798415

Abstract Details

2015, PhD, University of Cincinnati, Engineering and Applied Science: Electrical Engineering.
The kinetics of homogenization of binary melts in the As concentration range x ∈ (0%,50%) are followed using punctuated, off-line Raman profiling, and show that 2 gm sized melts in the range x ∈ (20%,30%) take nearly two weeks to homogenize when the starting materials are reacted at 700°C. The resulting research-grade Arsenic-Selenide glasses are the most compositionally homogeneous glasses produced thus far. The enthalpy of relaxation at Tg (glass transition temperature) -ΔHnr(x) – shows a minimum in x ∈ (29%,37%) in aged samples. In such homogeneous glasses, molar volumes vary non-monotonically with composition and the fragility index m displays a broad global minimum in x ∈ (20%,40%) where m < 20. The super-strong nature of melt compositions in x ∈ (20%,40%) hinders melt diffusion at high temperatures, leading to the observed slow kinetics of melt homogenization. In comparing these results with earlier reports, there is evidence that fragility decreases as melts are homogenized. Furthermore, a clear scaling of m vs. Tg is observed with a negative slope for Flexible glasses and a positive slope for Rigid and Stressed-rigid glasses, in contrast to expectations from some popular viscosity models. The Raman spectra of a large collection of As-Se glasses were analyzed and comparisons were made with the compositional profiles of the Raman modes of the P-Se alloy. For the first time, several key similarities between the systems are observed. The quasi-tetrahedral unit with a 4-fold coordinated Arsenic atom and the As-As homopolar ethylene-like unit are detected and compositional trends are observed to be similar to those of the P-Se system. As-As homopolar bond formation occurs at much lower than the chemical threshold of the system. The impact of the eutectic at As20Se80on the physical properties of the As-Se glasses are studied in great detail and a survey of other binary chalcogenide glasses is conducted and it is found that the eutectic region likely induces phase segregation of the compositions in the vicinity, leading to the smearing of compositional trends. The absence of the eutectic sharpens the observed topological phase boundaries. The Ge-As-Se ternary system in found to be significantly more influenced by the As atom than the Ge atom even in Ge-rich ternaries. Calorimetric and Raman spectroscopic studies reveal that the As atoms are likely both 3- and 4-fold coordinated and thus have a stronger influence on the network than the Germanium atoms, thus providing further evidence to support the existence of both the quasi-tetrahedral and Ethylene-like units. 119mSn Mossbauer spectroscopic studies reveal that - at least in the Ge-rich ternary - Ge-Ge homopolar bonds form near the computed chemical threshold.
Punit Boolchand, Ph.D. (Committee Chair)
Bernard Goodman, Ph.D. (Committee Member)
Wayne Bresser, Ph.D. (Committee Member)
Marc Cahay, Ph.D. (Committee Member)
Peter Kosel, Ph.D. (Committee Member)
184 p.
Electrical Engineering
Eutectic effects; Ge-As-Se ternary; Quasitetrahedral structures; Ethylene-like units in As-Se binary glass; Mossbauer study of Ge-As-Se ternary; Ge-As-Se ternary intermediate phase

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Citations

  • Ravindren, S. (2015). New insights into the Glass Structure and Melt Dynamics of Ge-As-Se Alloys: Topological Phases, Eutectic Effects, Slow Homogenization of Melts and Nanoscale Phase Separation Effects [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427798415

    APA Style (7th edition)

  • Ravindren, Sriram. New insights into the Glass Structure and Melt Dynamics of Ge-As-Se Alloys: Topological Phases, Eutectic Effects, Slow Homogenization of Melts and Nanoscale Phase Separation Effects. 2015. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427798415.

    MLA Style (8th edition)

  • Ravindren, Sriram. "New insights into the Glass Structure and Melt Dynamics of Ge-As-Se Alloys: Topological Phases, Eutectic Effects, Slow Homogenization of Melts and Nanoscale Phase Separation Effects." Doctoral dissertation, University of Cincinnati, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427798415

    Chicago Manual of Style (17th edition)

ucin1427798415
593
© 2015, some rights reserved.Creative Commons License New insights into the Glass Structure and Melt Dynamics of Ge-As-Se Alloys: Topological Phases, Eutectic Effects, Slow Homogenization of Melts and Nanoscale Phase Separation Effects by Sriram Ravindren is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.