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DS: Fachverband Dünne Schichten

DS 40: Focus Session: Resistive Switching by Redox and Phase Change Phenomena VII (Optical properties and theory of PC materials)

DS 40.4: Talk

Thursday, April 3, 2014, 12:15–12:30, CHE 89

Vibrational Properties of Layered Tellurides from First-Principles Calculations — •Ralf Stoffel¹ and Richard Dronskowski^1,2 — ¹Institute of Inorganic Chemistry, RWTH Aachen University, 52056 Aachen — ²Jülich–Aachen Research Alliance (JARA)

We present recent results of density-functional theory (DFT) based calculations of the vibrational properties of layered tellurides, such as Sb₂Te₃ and several Ge_xSb_yTe_z (GST) compounds, using the ab initio force-constant method. The latter compounds are well-known phase-change materials on the pseudo-binary tieline GeTe–Sb₂Te₃, and they can be switched easily between amorphous and crystalline phases which significantly differ in their optical and electrical properties. Here, we discuss the thermodynamically stable hexagonal polymorphs of those GST phases. Common DFT approaches are known to fail in describing the weak, non-covalent Te–Te interactions within these layered structures. For that reason, we investigate the influence of dispersion-corrected DFT on the calculated properties. We discuss phonon properties such as band structures and densities of states as well as thermochemical data such as Gibbs free energies or heat capacities. Other derived properties will also be presented, for example Grüneisen and atomic displacement parameters. The reliability of the results is verified by comparing the theoretical data with experimental references obtained from nuclear inelastic scattering (NIS). Finally, we show how our results help to interpret experimental data, and also give a more detailed insight into the theoretical background.