Experimental and theoretical studies of phase-change Ge-Sb-Te alloys in the liquid state
Synthesis and Properties of Functional Materials
Final Report Abstract
This project has focused on the structural, electronic and kinetic properties of the liquid and slightly supercooled liquid phase of selected, prototypical phase-change materials. These materials have important applications in the field of non-volatile memories, neuro-inspired computing, and opto-electronic devices. State-of-the-art experimental techniques, such as high-energy synchrotron X-ray diffraction and neutron diffraction with isotopic substitution, ab initio molecular dynamics simulations based on density functional theory, and reverse Monte-Carlo simulations, have been employed for this investigation. Our work has elucidated the local structure of liquid and supercooled-liquid phase-change materials at the microscopic level. It has also shed light on the high diffusion coefficients and low viscosities of the supercooled liquid at elevated temperatures. This is a crucial property of phase-change materials for applications in non-volatile memories, since it enables fast crystallization upon an external stimulus and, thus, fast switching between the two states of the memory cell. In the last part of the project, the kinetic behaviour of the liquid in the deep supercooled regime has also been investigated. A liquid-liquid phase transition has been shown to occur in several phase-change materials at low temperature. Even more importantly, the transition has been shown to be responsible for a pronounced increase in the activation energy of viscosity, the so called fragile-to-strong crossover. This property is crucial for applications, since it dramatically increases the stability of the amorphous state at low temperatures. We expect that the understanding gained in this project will help the search for new phasechange materials with better switching properties.
Publications
- (2019) Femtosecond x-ray diffraction reveals a liquid-liquid phase transition in phase-change materials. Science (New York, N.Y.) 364 (6445) 1062–1067
Zalden, Peter; Quirin, Florian; Schumacher, Mathias; Siegel, Jan; Wei, Shuai; Koc, Azize; Nicoul, Matthieu; Trigo, Mariano; Andreasson, Pererik; Enquist, Henrik; Shu, Michael J.; Pardini, Tommaso; Chollet, Matthieu; Zhu, Diling; Lemke, Henrik; Ronneberger
(See online at https://doi.org/10.1126/science.aaw1773) - Structural, electronic and kinetic properties of the phase-change material Ge2Sb2Te5 in the liquid state. Scientific Reports 6, 27434 (2016)
M. Schumacher, H. Weber, P. Jóvári, Y. Tsuchiya, I. Kaban, and R. Mazzarello
(See online at https://doi.org/10.1038/srep27434) - Experimental and ab-initio molecular dynamics study of the structure and physical properties of liquid GeTe. Physical Review B 96, 054204 (2017)
H. Weber, M. Schumacher, P. Jóvári, Y. Tsuchiya, W. Skrotzki, R. Mazzarello, and I. Kaban
(See online at https://doi.org/10.1103/PhysRevB.96.054204) - Correlating ultrafast calorimetry, viscosity and structural measurements in liquid GeTe and Ge15Te85, Physical Review Materials 2, 0293405 (2018)
H. Weber, J. Orava, I. Kaban, J. Pries, and A.L. Greer
(See online at https://doi.org/10.1103/PhysRevMaterials.2.093405)
