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.
Highlights
Controlling a state of material between its crystalline and glassy phase has fostered many real-world applications
We explore the impact of systematic changes in chemical bonding on crystallization kinetics
Crystallization kinetics have been long known to differ for metals and covalently bonded solids
Summary
Controlling a state of material between its crystalline and glassy phase has fostered many real-world applications. Very recently has it become possible to reach the huge cooling rates needed to create a metallic glass even from an elemental metal[13] These differences in crystallization and vitrification between metallic and covalently bonded systems must be closely related to differences in the interaction between the atoms involved. Phase change materials have been identified as a class of materials whose crystalline states have a bonding mechanism different from metallic and covalent bonding types[15,16,17]. This immediately raises an intriguing question of whether crystallization of phase change materials shows differences from the crystallization of solids that utilize covalent or metallic bonding This question is of academic interest and relevant for applications.
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