Unraveling the Crystallization Kinetics of Supercooled Liquid GeTe by Ultrafast Calorimetry

Abstract

Crystallization kinetics of phase change materials (PCMs) at high temperatures is of key importance for the extreme speed of data writing and erasing. In this work, the crystallization behavior of one of the typical PCMs, GeTe, has been studied using ultrafast differential scanning calorimetry (DSC) at high heating rates up to 4 × 104 K s–1. A strong non-Arrhenius temperature-dependent viscosity has been observed. We considered two viscosity models for estimating the crystal growth kinetics coefficient (U kin). The results showed that the MYEGA model was more suitable to describe the temperature-dependent viscosity and the crystal growth kinetics for supercooled liquid GeTe. The glass transition temperature (T g) and fragility m were estimated to be 432.1 K and 130.7, respectively. The temperature-dependent crystal growth rates, which were extrapolated by the MYEGA model, were in line with the experimental results that were measured by in situ transmission electron microscopy at a given temperature. The crystal growth rate reached a maximum of 3.5 m s–1 at 790 K. These results based on ultrafast DSC with the MYEGA model offer a revelation for crystallization kinetics of supercooled liquid GeTe.

Resolving glass transition in Te-based phase-change materials by modulated differential scanning calorimetry

“…However, on the basis of the ultrafast DSC, Orava et al reported that m is ∼90 for GST, 2) and our previous study showed m of GeTe of ∼130. 27) Apparently, the present results of the fragility of PCMs are different from the previous ones. It may due to the fragile-to-strong transitions present in such Te-based supercooled liquids.…”

Correlating ultrafast calorimetry, viscosity, and structural measurements in liquid GeTe and Ge15Te85

“…%). Liquid GeTe was reported to be a high-fragility liquid with m ≈ 131 inferred from ultrafast differential scanning calorimetry (FDSC) [10], or m ≈ 104-111 by molecular-dynamic (MD) simulations [8]. Such a high fragility does not conform well to the relatively lower activation energy for crystal growth Q G = 171 kJ mol −1 [11] reported for GeTe in contrast to the value of Q G = 227 kJ mol −1 for GST [12].…”

Quantitative estimation of crystallization kinetics in GeGaS and Au‐doped GeGaS glass‐ceramics

“…This was also emphasized recently by Orava and Angell, they claimed the unreliable threshold of the heating rate is 10 000 K/s for the phase‐change material Ge 2 Sb 2 Te 5 . Figure shows the Johnson‐Mehl‐Avrami (JMA) numerical simulated DSC peaks with heating rates from 5 to 600 K/min (the JMA simulation is similar to previous works and the details are not shown here) and the corresponding crystallized fraction of GGS and GGS‐Au. We found that, there is only a very insignificant difference between T p and T 0.63 in GGS and GGS‐Au when the heating rate is 60 K/min, that is, being about 2 and 2.5 K, respectively.…”

“…On basis of the Stokes‐Einstein relation between U kin and viscosity η , for example, U kin ∝ η −1 , we can deduced the expression of U kin as,where C is a constant to indicate the difference between U kin and η −1 . In this work, we use MYEGA viscosity model to describe the temperature‐dependent viscosity η of supercooled liquid GGS and GGS‐Au.…”

“…Recently, the calorimetric methods with fast scanning rate were developed to study the crystallization kinetics of chalcogenide phase‐change materials . Using the Kissinger method and Mauro‐Yue‐Ellison‐Gupta‐Allan (MYEGA) viscosity model, the temperature‐dependent crystallization kinetics parameters and/or crystal growth rate in the material that crystallizes with one or more crystalline phases simultaneously, can well be estimated quantitatively . In the present paper, we prepared Au‐doped chalcogenide glasses to explore the effect of Au doping on the crystallization kinetics in the chalcogenide glass‐ceramics, and employed various differential scanning calorimetric methods together with the MYEGA viscosity model to estimate the crystal growth rate in Ge 26.7 Ga 8 S 65.3 and 0.1% Au‐doped Ge 26.7 Ga 8 S 65.3 supercooled liquids, and presented first quantitative evidence that Au doping can significantly reduce the crystallization rate in the glass‐ceramics.…”