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Molecular Structure and Intermediate Phases in Group-v Binary Chalcogenide Glasses

Georgiev, Daniel Georgiev
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1044541309

Abstract Details

2003, PhD, University of Cincinnati, Engineering : Electrical Engineering.
Chalcogenide glasses offer unique opportunities for basic science and technological applications. The physical properties of such network-forming glasses, including the glass-forming tendency, are intimately connected to global connectivity of their backbones. In particular, the elastic behavior of glasses leads to the existence of three distinct phases that appears to be generic in network forming systems. Weakly cross-linked networks are mechanically soft and form floppy phases . Optimally cross-linked networks lead to stress-free or self-organized networks, and are identified with intermediate phases . Strongly cross-linked networks are mechanically stiff and usually form part of stressed-rigid phases . The floppy-intermediate and stressed-rigid classification of the group V chalcogenides is recognized in this work for the first time. The glass systems examined include P-Se, As-Se, and As-S. Thermally reversing windows (glass compositions wherein T g become almost completely reversing) are observed in the three binary glass systems using temperature-Modulated Differential Scanning Calorimetry (MDSC), and are identified with the opening of (non-mean-field) intermediate phases. The molecular structure of these glasses is studied by Raman scattering, MDSC and 31 P NMR, and the local structures responsible for intermediate phases are identified with assistance from constraint counting procedures. Raman scattering and Nuclear Magnetic Resonance (NMR) results on P-Se glasses provide compelling evidence for existence of four-fold coordinated phosphorous species that are bonded to three bridging and one terminal selenium, Se=P(Se 1/2 ) 3 . The structure results provide a basis to quantitatively understand compositional trends in T g in the stochastic agglomeration limit. The existence of analog four-fold coordinated As species is suggested by MDSC experiments on As-Se glasses. Our experimental results also show that stressed-rigid phases in the examined glasses are usually phase separated on a molecular level. Phase separation initiates near the stoichiometric composition, As 2 S 3 , and grows as the As content, x , of binary As x S 1-x glasses exceeds 0.38. Similar behavior has been observed in As-Se and P-Se glasses. A new understanding of global maxima in glass transition temperatures near stoichiometric compositions has emerged. These maxima are the result of a decrease in network connectivity as the backbone nano-scale phase separates.
Dr. Punit Boolchand (Advisor)
172 p.
chalcogenide glasses; raman; MCSC; intermediate phase; molecular structure

Recommended Citations

Citations

  • Georgiev, D. G. (2003). Molecular Structure and Intermediate Phases in Group-v Binary Chalcogenide Glasses [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1044541309

    APA Style (7th edition)

  • Georgiev, Daniel. Molecular Structure and Intermediate Phases in Group-v Binary Chalcogenide Glasses. 2003. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1044541309.

    MLA Style (8th edition)

  • Georgiev, Daniel. "Molecular Structure and Intermediate Phases in Group-v Binary Chalcogenide Glasses." Doctoral dissertation, University of Cincinnati, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1044541309

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.