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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mater. | doi: 10.3389/fmats.2019.00069

Linking Melt dynamics with Topological Phases and molecular structure of Sodium Phosphate glasses from Calorimetry, Raman scattering and Infrared reflectance.

  • 1University of Cincinnati, United States
  • 2University of California, Los Angeles, United States
  • 3Sorbonne Universités, France

A score of especially dry and homogeneous (Na2O)x(P2O5)100-x glass compositions over a wide range, 0 < x < 61%, are synthesized and examined in Modulated-DSC, Raman scattering, Infrared Reflectance and Molar volume experiments. The glass transition temperature variation, Tg(x) displays three regimes; at low x (0 < x < 15%), Na serves as a network modifier. At higher x, 15% < x < 50%, Na serves as a network former, as chains of Q2 species steadily grow and Tg(x) increases. In this regime, we observe a square-well like, thermally reversing window, bordered by abrupt rigidity transition near, xr = 37.5% and stress transition, near xs = 46.0% defining the Intermediate Phase (IP). The rigidity transition near xr = 37.5% occurs near the percolation of rigidity predicted by the Coarse Graining model. Variations of melt fragility index, m(x), established from complex Cp measurements show m(x =0) to be 15(1), and to increase monotonically with x to display a square-well-like fragility window (m < 20) in the 37.5(3)% < x < 46.0(2)% range, a range which coincides with the reversibility window. These results show that melt dynamics encode glass topological phases. At still higher x (> 50%), Tg(x) mildly decreases with increasing x, as pyrophosphate units decouple from the backbone and glasses segregate. Raman scattering measurements show that the fraction of the local structural species, f(Q3(x)), f(Q2(x)) and f(Q1(x)) track the mean-field behavior based on glass stoichiometry (x), as noted earlier from 31P NMR experiments. Raman scattering also shows that the Q2 structural species always display a triad of modes, a majority mode and two satellite modes that serve as topological defects. For the two highest frequency optic modes, Infrared specular reflectance measurements show that the frequency difference between the Longitudinal Optic (LO) and Transverse Optic (TO) response displays a global minimum in the IP. The local minimum of molar volumes, a global minimum in the LO-TO mode splitting, a fragility window that coincides with the reversibility window, each observation provides persuasive evidence of the singular role of the IP in present glasses.

Keywords: Raman Scattering, Modulated DSC (MDSC), Topological phases, Reversibility window, Fragility Window, Volumetric Window, Infrared reflectance, Longitudinal optical (LO) phonon scattering, Transverse optical (TO) phonon scattering, Topological Constraint Theory (TCT), Intermediate phase

Received: 21 Feb 2019; Accepted: 01 Apr 2019.

Edited by:

Jincheng Du, University of North Texas, United States

Reviewed by:

Stefan Karlsson, RISE Glass section, RISE Research Institutes of Sweden, Sweden
William LaCourse, Alfred University, United States  

Copyright: © 2019 Mohanty, Mandal, Gogi, Chen, Novita, Chbeir, Bauchy, Micoulaut and Boolchand. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Punit Boolchand, University of Cincinnati, Cincinnati, United States, boolchp@ucmail.uc.edu