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What Do We Still Want to Know 90 Years After...
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What Do We Still Want to Know 90 Years After the Continuous Random Network (CRN) Theory?

A special issue of Ceramics (ISSN 2571-6131).

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 11171

Special Issue Editors

Prof. Dr. Michael I. Ojovan

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Guest Editor
Department of Materials, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK
Interests: amorphous and crystalline materials; glass transition; vitrification; nuclear waste management; immobilisation; radiation effects
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Yuanzheng Yue

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Guest Editor
Department of Chemistry and Bioscience, Aalborg University, 9220 Aalborg, Denmark
Interests: glass materials for electrodes and electrolytes in Li/Na ion batteries
Dr. Shangcong Cheng

E-Mail Website
Guest Editor
National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
Interests: the nature of glass state and glass transition; the relationship between microstructures and properties of glasses and ceramics; transmission electron microscopy; electron energy loss spectroscopy

Special Issue Information

Dear Colleagues,

In October 1932, almost 90 years ago, WH Zachariasen published his paper “The Atomic Arrangement in Glass”. Since then, CRN theory has become the most common model for the structure of glasses. While the theory is not challenged for its description of the short-range and long-range structure, glass structure in the medium range (0.5–2 nm) is still a controversial topic, and it has triggered many debates in the scientific community. It is difficult to know how much the progress of glass science has been hindered by the lack of knowledge of atomic arrangements in the medium range. Perhaps, the medium-range structure of glass plays a vital role in the nature of the glass state and its physical and chemical properties.

As the 90th anniversary of Zachariasen's famous paper approaches, this Special Issue will focus on the medium-range structures in glasses, its characterization, formation, and its relation with physical properties. Full research articles, short communications, and comprehensive reviews are welcome.

The proposed topics include but are not limited to the following:
-Characterization of structures of various glasses by advanced structural probes (X-ray and neutrons scattering, TEM, EXAFS, NMR, XANES, Raman spectroscopy, EELS);
-Understanding the glass formation process (inhomogeneities in glasses, clusters formations, correlation between viscosity-temperature relations with the evolution of structure of glasses, influence of cooling rates on properties, etc.);
-Influence of glass structures on its physical properties (brittleness of bulk glasses, high strength of glass fibers, anomalous low thermal expansion coefficient of silica glass).

Prof. Dr. Michael I. Ojovan
Prof. Dr. Yuanzheng Yue
Dr. Shangcong Cheng
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Ceramics is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Continuous random network theory
  • Medium-range structure
  • Cluster forming
  • Local ordering
  • Entropy changes
  • Nature of glass transition

Published Papers (3 papers)

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Research

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29 pages, 3411 KiB  
Article
Microscopic-Phenomenological Model of Glass Transition and Temperature Dependence of Viscosity—Part I: Foundations of the Model
by Karl Günter Sturm
Ceramics 2021, 4(2), 302-330; https://doi.org/10.3390/ceramics4020024 - 08 Jun 2021
Viewed by 2693
Abstract
The glass transition is described as a time- and history-independent singular event, which takes place in an interval dependent on the distribution width of molecular vibration amplitudes. The intrinsic glass transition is not seen as a relaxation phenomenon, but is characterized by a [...] Read more.
The glass transition is described as a time- and history-independent singular event, which takes place in an interval dependent on the distribution width of molecular vibration amplitudes. The intrinsic glass transition is not seen as a relaxation phenomenon, but is characterized by a fixed volumetric state at the glass temperature Tg0. The relaxation behavior of the transport properties depends on the distance to Tg0. Free volume is redefined and its generation is the result of the fluctuating transfer of thermal energy into condensed matter and the resulting combined interactions between the vibration elements. This creates vacancies between the elements which are larger than the cross-section of an adjacent element or parts thereof. Possible shifts of molecules or molecular parts through such apertures depend on the size and axis orientation and do not require further energetic activation. After a displacement, additional volume is created by delays in occupying abandoned positions and restoring the energetic equilibrium. The different possibilities of axis orientation in space result in the different diffusive behavior of simple molecules and chain molecules, silicate network formers, and associated liquids. Glass transformation takes place at a critical volume Vg0 when the cross-section of apertures becomes smaller than the cross-section of the smallest molecular parts. The glass transition temperature Tg0 is assigned to Vg0 and is therefore independent of molecular relaxation processes. Tg0 is well above the Kauzmann and Vogel temperatures, usually just a few degrees below the conventionally measured glass temperature Tg(qT). The specific volume at the two temperatures mentioned above cannot be achieved by a glass with an unordered structure but only with aligned molecular axes, i.e. in a crystalline state. Simple liquids consisting of non-spherical molecules additionally alter their behavior above Vg0 at Vgl where the biggest gaps are as small as the largest molecular diameter. Tgl is located in the region of the crystalline melting point Tm. Both regions, above and below Tm, belong to different physical states and have to be treated separately. In the region close to Vg0 respectively Tg0, the distribution of vibration amplitudes has to be taken into account. The limiting volume Vg0 and the formation of apertures larger than the cross-section of the vibrating elements or parts thereof, in conjunction with the distribution width of molecular vibrations as Vg0 is approached, and the spatial orientation of the molecular axes is key to understanding the glass transition. Full article
(This article belongs to the Special Issue What Do We Still Want to Know 90 Years After the Continuous Random Network (CRN) Theory?)
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14 pages, 3984 KiB  
Article
New Interpretation of X-ray Diffraction Pattern of Vitreous Silica
by Shangcong Cheng
Ceramics 2021, 4(1), 83-96; https://doi.org/10.3390/ceramics4010008 - 13 Mar 2021
Cited by 6 | Viewed by 3550
Abstract
The striking feature of X-ray diffraction pattern of vitreous silica is that the center of its intense but broad ring is located at nearly the same position as the strongest diffraction ring of β-cristobalite. Two fundamentally different explanations to the diffraction patterns were [...] Read more.
The striking feature of X-ray diffraction pattern of vitreous silica is that the center of its intense but broad ring is located at nearly the same position as the strongest diffraction ring of β-cristobalite. Two fundamentally different explanations to the diffraction patterns were appeared about 90 years ago, one based on the smallest crystals of β-cristobalite and the other based on the non-crystalline continuous random network. This work briefly outlines the facts supporting and objecting these two hypotheses, and aims to present a new interpretation based on a medium-range ordering structure on the facets of clusters formed in the glass transition process. It will be shown that the new interpretation provides a more satisfactory explanation of the diffraction pattern and physical properties of silica glass, and offers considerable valuable information regarding the nature of glass and glass transition. Full article
(This article belongs to the Special Issue What Do We Still Want to Know 90 Years After the Continuous Random Network (CRN) Theory?)
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Review

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14 pages, 1713 KiB  
Review
The Modified Random Network (MRN) Model within the Configuron Percolation Theory (CPT) of Glass Transition
by Michael I. Ojovan
Ceramics 2021, 4(2), 121-134; https://doi.org/10.3390/ceramics4020011 - 29 Mar 2021
Cited by 17 | Viewed by 3688
Abstract
A brief overview is presented of the modified random network (MRN) model in glass science emphasizing the practical outcome of its use. Then, the configuron percolation theory (CPT) of glass–liquid transition is concisely outlined, emphasizing the role of the actual percolation thresholds observed [...] Read more.
A brief overview is presented of the modified random network (MRN) model in glass science emphasizing the practical outcome of its use. Then, the configuron percolation theory (CPT) of glass–liquid transition is concisely outlined, emphasizing the role of the actual percolation thresholds observed in a complex system. The MRN model is shown as an important tool enabling to understand within CPT the reduced percolation threshold in complex oxide systems. Full article
(This article belongs to the Special Issue What Do We Still Want to Know 90 Years After the Continuous Random Network (CRN) Theory?)
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