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Direct evidence for abrupt rigidity and stress transitions in dry and homogeneous bulk GexSe100-x glasses

Bhosle, Siddhesh V.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307106143

Abstract Details

2011, MS, University of Cincinnati, Engineering and Applied Science: Electrical Engineering.
We introduce a Raman profiling method to track heterogeneity of melts over days as starting materials are reacted and batch compositions homogenize. Results on 2 gram sized dry GexSe100-x melts, reacted at 950°C, show that they homogenize on a scale of 10 microns after 168 hours in a process that has two steps. In the first step, elements of local structure evolve, followed by extended range structures forming as the Ge/Se stoichiometry across a batch composition equalizes by a slow diffusive process with a Diffusion constant, D = 2 x 10-6 cm2/sec. Such homogenization is precursive to self-organization. We have synthesized 21 glass compositions spanning the range, 10% < x < 33.33%, and have examined their thermal, optical and mechanical behavior in modulated DSC, Dispersive Raman scattering and Molar volume experiments respectively. These data, on glasses of unprecedented homogeneity, reveal sharply defined rigidity transition near xc (1) = 19.5(5)% and stress transition near xc(2) = 26.0(5)%, with optical elastic power-laws in the Intermediate Phase (IP: 19.5% < x < 26.0%) of p1 = 1.10(10), and in the Stressed rigid phase (x > 31.5%) of p2 = 1.50(3). The variation of non-reversing enthalpy, ΔHnr(x), at Tg is found to display three regimes, a global minimum (~0) in the IP, and an increase outside the IP, but with sharply defined walls at xc (1) and xc(2), the two elastic thresholds deduced from optical measurements. Variation of Molar volumes, Vm(x), also displays three regimes of behavior with a global minimum in the IP and an increase outside that phase. The ΔHnr term ages over weeks outside the IP glass compositions but not inside the IP. The variation of glass transition temperature, Tg(x) in the 10% < x < 33.33% range is well described by a polynomial. A sharp cusp in ΔHnr(x) term is observed near x = 31.5(5)% , and it coincides with a maximum in the slope of Tg with x, features that we identify with the first appearance of Ge-Ge bonds with increasing x, and demixing from the network backbone. In the composition range, 31.5% < x < 33.33%, glasses are viewed as being nanoscale phase separated into Se-rich and Ge-rich regions for which substantial evidence comes from Raman and Mössbauer spectroscopy experiments. The fraction R(x) of Edge-Sharing to Corner-Sharing tetrahedra, is found to increase in the 0.20 < R(x) < 0.37 range with x in the 20% < x < 33.33% range, in harmony with neutron scattering results. Melts containing traces of water synthesized at select compositions homogenize much quicker than their dry counterparts, however their physical properties including Tg, ΔHnr, Vm are measurably different from their dry counterparts. The intrinsic physical behavior of dry and homogeneous chalcogenides glasses can vary sharply with composition near elastic and chemical phase transitions, showing that the physics of network glasses may be far more interesting than hitherto recognized.
Punit Boolchand, PhD (Committee Chair)
Bernard Goodman, PhD (Committee Member)
Darl McDaniel, PhD (Committee Member)
Marc Cahay, PhD (Committee Member)
Altan Ferendeci, PhD (Committee Member)
118 p.
Condensation
Intermediate Phase; Reversibility window; Raman profiling; Germanium-Selenium glasses; homogenization; mDSC

Recommended Citations

Citations

  • Bhosle, S. V. (2011). Direct evidence for abrupt rigidity and stress transitions in dry and homogeneous bulk GexSe100-x glasses [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307106143

    APA Style (7th edition)

  • Bhosle, Siddhesh. Direct evidence for abrupt rigidity and stress transitions in dry and homogeneous bulk GexSe100-x glasses. 2011. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307106143.

    MLA Style (8th edition)

  • Bhosle, Siddhesh. "Direct evidence for abrupt rigidity and stress transitions in dry and homogeneous bulk GexSe100-x glasses." Master's thesis, University of Cincinnati, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307106143

    Chicago Manual of Style (17th edition)

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© 2011, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.