What is it about?
Glasses and crystals are the two most important forms of solids. For a given stoichiometry, it is usually found that the glass and the corresponding crystal have a very similar short-range order, but only the crystalline phase also possesses long-range order. The similarity of short-range order has long been assumed to be due to a similarity in chemical bonding. Here we show that indeed for most solids the glasses employ the same bonding as the corresponding crystals. Yet, for some solids the bonding and hence also the short-range order and the properties differ substantially between glass and crystalline phase. This behavior is only found for those glasses, where the crystals employ an unconventional bonding mechanism, called metavalent bonding. Employing tools of quantum mechanics allows the physicists to draw a ‘treasure map’ identifying those solids.
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Why is it important?
This enables the rapid identification of solids, which drastically change their properties upon crystallization, a property which is important for a variety of applications.
Perspectives
In 1932, W.H. Zachariasen wrote a thought-provoking article. He studied the atomic arrangement of oxide glasses and argued that the short range order is the same as the corresponding crystal. He also provided a reason for this similarity. He expressed that the forces holding the atoms together are the same in both cases. We would now say that chemical bonding is very similar in both cases. More than 90 years later, the tools are available to verify this hypothesis. Indeed, his assumption is perfectly right for oxide glasses like SiO2. Amazingly, however, there are some solids where the glasses have a rather different atomic arrangement, properties and bonding. These glasses form crystals which employ an unconventional bonding mechanism, called metavalent bonding. We have been working in team for about 4 years to develop this manuscript. It is highly rewarding to now finally cross the finish line and publish this manuscript.
Matthias Wuttig
Rheinisch Westfalische Technische Hochschule Aachen
Read the Original
This page is a summary of: Tailoring chemical bonds to design unconventional glasses, Proceedings of the National Academy of Sciences, January 2024, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2316498121.
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