Crystallization and Vitrification Kinetics by Design: The Role of Chemical Bonding

TL;DR

This study reveals how the chemical bonding nature and stoichiometry in phase change materials influence crystallization and vitrification speeds, providing a predictive framework for material design.

Contribution

It identifies stoichiometry and bonding type as key factors controlling crystallization kinetics, offering a quantum-chemical map for designing materials with desired phase change properties.

Findings

Covalency slows crystallization by six orders of magnitude.

Crystallization speed depends on stoichiometry and bonding type.

Quantum-chemical map explains trends and guides material design.

Abstract

Controlling a state of material between its crystalline and glassy phase has fostered many real-world applications. Nevertheless, design rules for crystallization and vitrification kinetics still lack predictive power. Here, we identify stoichiometry trends for these processes in phase change materials, i.e. along the GeTe-GeSe, GeTe-SnTe, and GeTe-Sb2Te3 pseudo-binary lines employing a pump-probe laser setup and calorimetry. We discover a clear stoichiometry dependence of crystallization speed along a line connecting regions characterized by two fundamental bonding types, metallic and covalent bonding. Increasing covalency slows down crystallization by six orders of magnitude and promotes vitrification. The stoichiometry dependence is correlated with material properties, such as the optical properties of the crystalline phase and a bond indicator, the number of electrons shared between adjacent atoms. A quantum-chemical map explains these trends and provides a blueprint to design crystallization kinetics.