Student project/master thesis: Strain-tuning of the new class of hyperferroelectrics based on density functional theory (DFT)

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.

Tasks:

• Run DFT/Density Functional Pertubation Theory (DFPT) simulations using the abinit package
• Write python scripts
• Process and analyze data

What you will learn:

• Running DFT/DFPT simulations in abinit
• Phonon calculations
• Python for data analysis
• Physics of ferroelectrics

Contact

Prof. Dr. Anna Grünebohm or Susanne Kunzmann

References

[1] Kevin F. Garrity, Karin M. Rabe, and David Vanderbilt. Hyperferro-
electrics: Proper ferroelectrics with persistent polarization. Phys. Rev. Lett.,
112:127601, Mar 2014.
[2] Anubhav Jain, Shyue Ping Ong, Geoffroy Hautier, Wei Chen,
William Davidson Richards, Stephen Dacek, Shreyas Cholia, Dan Gunter,
David Skinner, Gerbrand Ceder, and Kristin A. Persson. Commentary: The
materials project: A materials genome approach to accelerating materials
innovation. APL Materials, 1(1):011002, 2013.

Student Project: Effect of thin-film thickness on domain wall dynamics under ultrafast field application in BaTiO₃

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].

References

[1] Ruben Khachaturyan, Aris Dimou, Anna Grünebohm, Domain wall acceleration by ultrafast field ramping and non-equilibrium dipoles dynamics: an ab initio based molecular dynamics study, arXiv:2109.10062
[2] A. Grünebohm, M. Marathe, Impact of domains on the orthorhombic-tetragonal transition of BaTiO3: An ab initio study, Phys. Rev. B 114417, 2020

Contact: Prof. Dr. Anna Grünebohm or Sheng-Han Teng

Student project/master thesis: Functional responses of ferroelectric composites: an ab initio based study on interface strain

In this project we investigate the impact of interface strain on the functional responses of ferroelectric composites.

Ferroelectric perovskites are widely used in applications and are promising for energy harvesting as well as for future efficient solid-state cooling devices. All applications share the following demands on materials design: Replace toxic Pb and increase efficiency of the functional responses in a broad and suitable operation range. In this quest, ferroelectric composites came into focus as they can be optimized by the choice of different constituents and their morphologies.

Recently we have shown how one may optimize the electrocaloric response of BaTiO₃ films by biaxial strain in the (001)-plane. Thereby the domain structure of the film plays a crucial role. The task of this project is to extend this study to different crystallographic directions and solid solutions of (Ba,Sr)TiO₃. We will explore the temperature-strain phase diagrams of and the stability of specific elastic domain structures. For this purpose we will perform coarse-grained molecular dynamics simulations employing the feram code.

Contact: Prof. Dr. Anna Grünebohm. Email: anna.gruenebohm@rub.de

Student Project: Domain wall propagation

In this project you will use molecular dynamic (MD) simulation to simulation domain wall (DW) propagation in ferroelectric crystals under an external electric field. Analysis of local polarizations and its collective behavior will be done using Python.

Contact Prof. Dr. Anna Grünebohm or Sheng-Han Teng.