Lattice dynamics in 2D layered transition metal oxides and sulfides: First-principles study

Nina Mattila

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

The constant development of new technologies and finiteness of natural resources along with increasing ecological responsibility create an impetus to search not only for alternative energy resources but also for more rational utilization of existing energy supplies. Thermoelectric materials are an encouraging tool in terms of waste heat harvesting due to their ability to generate electric current as a response to the temperature gradient. This thesis presents a summary of an investigation into the themoelectric properties of the transition metal disulfides TiS₂, ZrS₂ and HfS₂ and alkali metal intercalated cobalt dioxides LiₓCoO₂ and NaₓCoO₂, (x=0, 0.5 and 1). These materials are repre- sentatives of a layered 2D materials class that has a high potential in thermoelectric applications. The materials were studied using a first-principles DFT hybrid PBE0 functional as the main investigating tool, while the weak van der Waals interaction was taken into account via DFT-D3 dispersion correction. Particular attention was paid to the materials’ lattice dynamics and lattice thermal conductivity – one of the most crucial parameters affecting thermoelectric performance. The data obtained was analyzed and presented in such a way that the reader could follow the change in material properties with respect to the transition metal atom inside the layer for the MS₂ case and the alkali metal intercalated between the layers for the MₓCoO₂ case Obtained results are in a good agreement with available literature and showed that structurally isotypic compounds can exhibit rather different properties due to the nature of bonding (in the MS₂ case) and type of the intercalated atom (in the MₓCoO₂ case). The chosen level of theory has demonstrated high reliability for describing the electronic and vibrational properties of the studied 2D systems with without any system-dependent parametrization. In terms of lattice dynamics, the study revealed the importance of taking into account all the components of the lattice thermal conductivity in a complex to obtain the full picture and find the origin for the difference between materials. Additionally, phonon anharmonicity exerts a rather strong effect; therefore, careful consideration of point defects (vacancies) and higher-order anharmonic terms might be the next step to enhance the calculations.
Translated title of the contributionLattice dynamics in 2D layered transition metal oxides and sulfides: First-principles study
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Karttunen, Antti, Supervising Professor
Publisher
Print ISBNs978-952-64-0035-8
Electronic ISBNs978-952-64-0036-5
Publication statusPublished - 2020
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • lattice dynamics
  • metal oxides
  • sulfides

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