Pressure-driven transformation of the ordering in amorphous network-forming materials

Anita Zeidler and Philip S. Salmon

Phys. Rev. B 93, 214204 – Published 22 June 2016

Abstract

The pressure-induced changes to the structure of disordered oxide and chalcogenide network-forming materials are investigated on the length scales associated with the first three peaks in measured diffraction patterns. The density dependence of a given peak position does not yield the network dimensionality, in contrast to metallic glasses where the results indicate a fractal geometry with a local dimensionality of $≃ 5 / 2$ . For oxides, a common relation is found between the intermediate-range ordering, as described by the position of the first sharp diffraction peak, and the oxygen-packing fraction, a parameter that plays a key role in driving changes to the coordination number of local motifs. The first sharp diffraction peak can therefore be used to gauge when topological changes are likely to occur, events that transform network structures and their related physical properties.

Received 2 September 2015
Revised 29 March 2016

DOI:https://doi.org/10.1103/PhysRevB.93.214204

Physics Subject Headings (PhySH)

Network structure Pressure effects

Amorphous materials Chalcogenides Oxides

Pressure techniques X-ray diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Anita Zeidler and Philip S. Salmon

Department of Physics, University of Bath, Bath, BA2 7AY, United Kingdom

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Issue

Vol. 93, Iss. 21 — 1 June 2016

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Images

Figure 1
Representative structure factors $S (k)$ , as measured at ambient pressure by neutron diffraction (ND) [solid curves] or x-ray diffraction (XRD) [broken (red) curves] and plotted in terms of the scaled scattering vector $k d$ , for a bulk-metallic glass ${Pd}_{42.5} {Ni}_{7.5} {Cu}_{30} P_{20}$ [ $d = 2.656$ Å (ND) or $d = 2.739$ Å (XRD)], for a network-forming chalcogenide glass ${GeSe}_{2}$ ( $d = 2.363$ Å), for a network-forming oxide glass ${SiO}_{2}$ ( $d = 1.599$ Å), and for elemental glassy Se ( $d = 2.349$ Å). The ND and XRD $S (k)$ functions for ${GeSe}_{2}$ and the ND $S (k)$ function for ${SiO}_{2}$ show a “three-peak” structure that is typical of network-forming materials, where the approximate positions of these peaks as labeled by $k_{1}$ , $k_{2}$ , and $k_{3}$ are indicated by the vertical broken lines. A principal peak at $k_{2}$ is absent in the XRD $S (k)$ function for ${SiO}_{2}$ (see the text). For the metallic glass, ordering does not appear on a length scale associated with either $k_{1}$ or $k_{2}$ and the magnitude of $S (k)$ has been halved for clarity of presentation. For Se, ordering does not appear on a length scale associated with $k_{1}$ .
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Figure 2
The reduced density $ρ / ρ^{0}$ dependence of the scaled (a) peak position $k_{3} / k_{3}^{0}$ , (b) principal peak position $k_{2} / k_{2}^{0}$ , and (c) FSDP position $k_{1} / k_{1}^{0}$ as measured by using in situ high-pressure x-ray or neutron diffraction for materials under compression. In (a) the solid curve corresponds to $D_{3} = 5 / 2$ and accounts for the metallic glass data taken from Refs. [16, 23], and the chained and broken curves correspond to $D_{3}$ values of 6 and $- 10$ , respectively. In (b) the solid curve corresponds to $D_{2} = 1.82$ , and the broken curve corresponds to $D_{2} = 5$ . The vertical arrows indicate (from left to right) the reduced densities at which the coordination number ${\bar{n}}_{AO}$ of the local motifs in glassy ${GeO}_{2}$ , $B_{2} O_{3}$ , and ${SiO}_{2}$ starts to exceed its ambient pressure value of 4, 3, or 4, respectively. In (c) the solid and broken curves correspond to $D_{1}$ values of 10/9 and 5/3, respectively, and bracket most of the measured data points. The horizontal and vertical error bars on several of the data points give representative uncertainties.
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Figure 3
The dependence of the scaled FSDP position $k_{1} / k_{1}^{0}$ on (a) the oxygen-packing fraction $η_{O}$ and (b) the reduced oxygen-packing fraction $η_{O} / η_{O}^{0}$ for a variety of glassy and liquid oxides under compression. The horizontal and vertical error bars on several of the data points give representative uncertainties. In (b) the vertical arrows indicate (from left to right) the $η_{O} / η_{O}^{0}$ values at which the coordination number ${\bar{n}}_{AO}$ of the local motifs in glassy ${GeO}_{2}$ , $B_{2} O_{3}$ , and ${SiO}_{2}$ starts to exceed its ambient pressure value of 4, 3, or 4, respectively, and correspond to $η_{O}$ values of 0.59, 0.44, and 0.58, respectively. The inset shows only those data points for which ${\bar{n}}_{AO}$ retains its ambient pressure value, and the broken curve (also illustrated in the main panel) shows a fit to this data.
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