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Garrity et. al reported that ferroelectrics with LiGaGe structure, see Fig. 1 are not as sensitive to depolarization as compared to standard materials and coined the term hyperferroelectrics for this exciting observation [1]. These materials are particularly interesting for minitarization of ferroelectrics devices as they may show a ferroelectric instability in low dimensions. As so far only a few systematic studies exist, we will investigate the coupling between electronic and atomic structure for the prototypical hyperferroelectric material, NaZnSb via density functional theory and density functional perturbation theory.

Contact: Prof. Dr. Anna Grünebohm or Susanne Kunzman

The functional properties of ferroelectrics are governed by domain walls and their mobility. Recent studies reveal exotic properties like drastic domain wall acceleration and the effect of transient negative capacitance under an ultrafast field application as an intrinsic property of ferroelectrics. In this work, we will study how domain wall mobility is modified by the presence of an open interface and finite thickness of the ferroelectric film. We will use first-principal-based molecular dynamic simulations to investigate the impact of film thickness on domain wall dynamics. To do so, a microscopic analysis of local dipoles dynamics will be done, including statistical data analysis and its visualization. You will be supported in running molecular dynamics simulations and Python programming. During the project, you will gain knowledge about ferroelectric and statistical data analysis. See the literature to get insight into the topic [1] and investigate various domain walls using first-principle-based molecular dynamics [2].

Contact: Prof. Dr. Anna Grünebohm

Ferroelectric perovskites possess versatile functional properties and are used in a variety of modern electronic devices. In particular, the piezoelectric response of lead-free materials is of great interest in the field of sensors and energy harvesting [1]. Important challenges in this field are: How to enhance the mechanical strain response induced by the electric field and how to improve its temperature stability. This project focuses on the piezoelectric properties of solid solutions of BaTiO 3 –SrTiO 3 , where exceptionally large responses are possible at the three phase transitions (tetragonal, orthorhombic and rhombohedral phases) whose temperature can be adjusted by the compositions (see Fig. 1a). Your task is to calculate the piezoelectric coefficient d 33 for various temperatures and compositions using the code Feram (http://loto.sourceforge.net/feram), and finally construct a contour plot (similar to Fig. 1b but for piezoelectric response). This plot allows to predict optimal Sr-concentrations for applications

Contact: Prof. Dr. Anna Grünebohm