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Structural and Topological Evolution in SiSe glasses: Results from 1D and 2D Si and Se NMR Spectroscopy 29
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Maxwell A. T. Marple, Ivan Hung, Zhehong Gan, and Sabyasachi Sen J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.7b01307 • Publication Date (Web): 03 Apr 2017 Downloaded from http://pubs.acs.org on April 4, 2017
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The Journal of Physical Chemistry
Structural and Topological Evolution in SixSe1-x glasses: Results from 1D and 2D 29Si and 77
Se NMR Spectroscopy
M. A. T. Marple1, I. Hung2, Z. Gan2, S. Sen1,*
1
Dept. of Materials Science & Engineering, University of California at Davis, Davis, CA 95616, USA
2
Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA
*corresponding author (email:
[email protected])
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Abstract The coordination environments of Si and Se atoms and their connectivity in binary SixSe1-x glasses with 0.05 ≤ x ≤ 0.33 are investigated using a combination of one- and two- dimensional 29
Si and 77Se nuclear magnetic resonance (NMR) and Raman spectroscopy. The high-resolution
correlated isotropic and anisotropic
29
Si and
77
Se NMR spectra allow for the identification and
quantitation of a variety of Si and Se environments. The results suggest that the structure of these glasses is characterized by a network with essentially perfect short-range chemical order, but with strong clustering at the intermediate-range. Initial addition of Si to Se results in crosslinking of Se chain segments with nanoclusters of corner- and edge-shared SiSe4/2 tetrahedra. These clusters percolate via coalescence near x ≥0.2 to finally form a low-dimensional network with high molar volume, at the stoichiometric composition (x=0.33) that is composed of chains of edge-sharing tetrahedra cross-linked by corner-shared tetrahedra.
This structural evolution is
shown to be consistent with the compositional variation of the glass transition temperature and the molar volume of these glasses.
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The Journal of Physical Chemistry
1. INTRODUCTION Chalcogenide glasses represent an important class of materials for a variety of technological applications in the fields of optoelectronics, energy storage, and remote sensing.1-3 Their optimization for desired performance necessitates the development of a fundamental understanding of the underlying relationship between their physical properties and atomic structure. Such studies have mostly focused in the past on selenides and sulfides of Ge, As, P and Si4-11 that form covalently bonded and predominantly chemically ordered networks that follow the 8−N coordination rule. One of the most extensively studied glass-forming systems in this regard is the binary GexSe1-x system. Recent studies have shown that GexSe1-x glasses with excess Se are characterized by a network of randomly connected –Se-Se-Se– chain elements and GeSe4 tetrahedra that ultimately evolves into a predominantly corner-shared network of GeSe4 tetrahedra in the stoichiometric GeSe2 composition with some edge-sharing and minor violation in chemical order.12-14
It may be noted here that corner-shared tetrahedral network is also
characteristic of a wide variety of stoichiometric AX2 (A = Si, Ge, Be; X = O, F) crystalline and amorphous compounds, while chlorides such as ZnCl2 and chalcogenides such as GeX2 (X = S, Se) are characterized by predominantly corner-sharing ZnCl4/2, GeS4/2 and GeSe4/2 tetrahedra with some degree of edge-sharing.15-18 In contrast, the structures of crystalline and amorphous SiX2 (X = S, Se) compounds display a rather different and unique topology resulting from extensive to exclusive edge-sharing between SiX4/2 tetrahedra.9,
19-22
For example, the high-
temperature crystalline form of SiSe2 is composed of chains of doubly edge sharing SiSe4/2 tetrahedra, while the low-temperature polymorph contains tetrahedral chains composed of four edge-sharing tetrahedra that are cross-linked to one another via corner sharing.23 However, compared to the GexSe1-x glasses, little is known regarding the compositional evolution of the 3 ACS Paragon Plus Environment
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structural and topological characteristics of their isoelectronic analogues in the SixSe1-x system, although the nearest neighbor coordination environments of the constituent atoms are known to be similar in both glass-forming systems. Much of the early structural studies of SixSe1-x glasses focused on compositions near the stoichiometric SiSe2. Tenhover et al., on the basis of Raman spectroscopic measurements, concluded the presence of edge-sharing SiSe4/2 tetrahedra and significant intermediate range order in SiSe2 glass structure
9, 24
. Griffiths25 proposed the cross-linked-chain-cluster (CLCC)
model to interpret the Raman spectrum of the SiSe2 glass, where the structure was described to contain edge-sharing tetrahedral chain clusters that are cross-linked by corner-sharing tetrahedra. This structural moiety in the CLCC model is similar to that present in the low-temperature polymorph of SiSe2.23 Subsequent experimental studies and density functional theory (DFT) calculations provided support to the CLCC model.26-27 These studies suggest that the average tetrahedral chains in SiSe2 contain three SiSe4/2 tetrahedra (Fig. 1). The structure at low Si content (x
