Lattice dynamics in perovskites for green energy applications: A theoretical perspective
Licentiate thesis, 2022

Electrolyzers and fuel cells are used in green energy applications, electrolyzers split water to produce hydrogen, which can then be used in fuel cells to produce energy. Oxide perovskites have shown favorable properties for applications in this area, e.g., as electrolyte and cathode material in fuel cells and electrolyzers. The important property is the conductivity of protons, which depends sensitively on the hydrogen concentration and mobility. The concentration depends on the efficiency of the hydration reaction, which is the primary way to incorporate protons in perovskites. An example of an excellent proton conductor is acceptor doped BaZrO3. Hence, some of the most crucial material properties derive from defect properties. This thesis also explore the halide perovskites CsPbBr3, which have proven to be auspicious for photovoltaics. Insights into phase stability, phase transitions and the underlying dynamics in these materials are crucial. Thus, the understanding of microscopic properties is the cornerstone of this thesis.

In the present thesis, density functional theory is utilized to obtain training data for construction of potentials. The potentials that have been used are either force constant potentials or neural network potentials. The potential are then used to run lattice dynamics. To vastly extend the total simulation time or simply decrease the computational time, graphical processing units are also employed. Furthermore, defect models are applied to understand reaction kinetics.

More specifically, the vibrational defect thermodynamics of BaZrO3 was examined within the harmonic approximation. We also elaborate on the soft antiferrodistortive phonon mode found in this material using self-consistent phonons and molecular dynamics. This soft mode, should ultimately be the deciding factor for which structure
BaZrO3 exhibit at low temperatures Similar methods were also employed to investigate phonon dynamics in the very anharmonic perovskite, CsPbBr3. These type of insights can, e.g., further guide the development of new materials by fine-tuning of properties.

density func- tional theory

perovskites

defects

lattice dynamics

thermodynamic modelling

force constants

oxides

PJ-salen
Opponent: Jochen Rohrer, Materials Modelling Division, Technical University Darmstadt, Germany

Author

Petter Rosander

Chalmers, Physics, Condensed Matter and Materials Theory

Rosander, P. Wahnström, G. Elaborating on the vibrational impact of defects on the hydration thermodynamics in BaZrO3

Rosander, P. Fransson, E. Milesi-Brault, C. Guennou, M. Wahnström, G. Anharmonicity of the antiferrodistortive soft mode in barium zirconate BaZrO3

Fransson, E. Rosander, P. Rahm, M. Tadano, T. Erhart, P. Transitioning from underdamped to overdamped dynamics in CsPbBr3: Probing the limit of the phonon quasi-particle picture

Proton- och hydridjon-ledning i perovskiter

Swedish Energy Agency (45410-1), 2018-01-01 -- 2021-12-31.

Areas of Advance

Energy

Materials Science

Roots

Basic sciences

Infrastructure

C3SE (Chalmers Centre for Computational Science and Engineering)

Subject Categories

Materials Chemistry

Condensed Matter Physics

Publisher

Chalmers

PJ-salen

Opponent: Jochen Rohrer, Materials Modelling Division, Technical University Darmstadt, Germany

More information

Latest update

10/25/2023