# Beyond geometry orders: uncovering bonding-heterogeneity-dominated structure-relaxation coupling in glasses

## TL;DR

This study shows that electronic interactions, not just geometry, control the behavior of amorphous materials like glasses.

## Contribution

The paper reveals that bonding heterogeneity, not geometric order, dominates structure-relaxation coupling in glasses.

## Key findings

- Two Pd-based glasses with similar geometries show different relaxations due to electronic structure differences.
- Weaker Cu–P bonds in Pd40Cu40P20 enable atomic motions, while stronger Ni–P bonds in Pd40Ni40P20 restrict them.
- Electronic interactions and bonding fluctuations are critical for glass dynamics beyond geometric packing.

## Abstract

The microstructure determines properties paradigm applies well to crystalline materials but struggles with amorphous systems. While researchers have long sought to link amorphous structures to macroscopic properties, traditional analyses focus on geometric packing, which our study reveals to be insufficient. We demonstrate this using two Pd-based metallic glasses, \documentclass[12pt]{minimal}
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$\rm {Pd}_{40}\rm {Cu}_{40}\rm {P}_{20}$\end{document} and \documentclass[12pt]{minimal}
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$\rm {Pd}_{40}\rm {Ni}_{40}\rm {P}_{20}$\end{document}, which exhibit nearly identical geometries but different secondary relaxations. Electronic structure analysis uncovers the key distinction: \documentclass[12pt]{minimal}
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$\rm {Pd}_{40}\rm {Cu}_{40}\rm {P}_{20}$\end{document} has weaker Cu–P bonds and a less developed covalent network, enabling string-like atomic motions that drive pronounced relaxation, whereas \documentclass[12pt]{minimal}
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$\rm {Pd}_{40}\rm {Ni}_{40}\rm {P}_{20}$\end{document}’s stronger Ni–P interactions create a more constrained network. These findings highlight the critical role of electronic interactions and bonding fluctuations—beyond geometry—in governing glass dynamics. By integrating experiments and deep-learning simulations, we bridge the gap between local bonding heterogeneity and macroscopic behavior, offering new design principles for amorphous materials that prioritize electronic structure over purely geometric order. This advances glass physics by emphasizing the need to incorporate chemical interactions into structural analyses.

Why do amorphous materials behave differently despite similar structures? This study shows that electronic interactions, rather than geometry alone, play a decisive role in controlling glass dynamics and properties.