PhD Defence by Javier Sanz Rodrigo

Principal supervisor
Associate Professor Andrea Crovetto, DTU Nanolab

Co-supervisor
Professor Eugen Stamate, DTU Nanolab

Professor Ivano Eligio Castelli, DTU Energi

Assessment committee
Professor Juan Maria Garcia Lastra, DTU Energy
Associate Professor Julia Wiktor, Chalmers University
Associate Professor Alexander Ganose, Imperial College London

Moderator at defence

Professor Thomas Willum Hansen, DTU Nanolab

Abstract

Phosphosulfides are materials that contain both phosphorus and sulfur, together with at least one metal. Even though they exist in many possible combinations, only a small part of all the combinations has been explored so far. In this thesis I study phosphosulfides using computer simulations, with the goal of understanding how their composition and structure influences the material’s properties.

A central part of the work is a large search across many different combinations of metals, phosphorus, and sulfur. For each candidate material, the calculations estimate whether it is likely to be stable and what its electronic behavior may be. By comparing hundreds of materials, clear patterns emerge. Some structures appear often because they are especially good at forming stable compounds, while other structural families are rare or difficult to stabilize. These patterns make it possible to make predictions: if a new phosphosulfide has a certain composition or structure type, it is often possible to anticipate whether it is likely to be stable and whether it is more likely to behave like a metal or like a semiconductor.

To connect these general trends to real materials, the thesis includes a detailed study of one particular phosphosulfide that stands out in the screening. For this material, I analyze its properties in much greater depth and compare the computational results with measurements performed by collaborators on thin films. This combination of theory and experiment helps test whether the predictions capture the real behavior of the material and helps explain why it behaves the way it does.

Finally, the thesis looks beyond the structures that are already known for phosphosulfides. Many potentially interesting phosphosulfides may not have been discovered simply because nobody has looked for the right atomic arrangements. To address this, I propose new candidate structures by borrowing “templates” from related families of materials and adapting them to phosphosulfides. This produces a set of possible new phosphosulfides that are not currently reported. One of these candidates is then studied in detail, focusing on whether it should be stable and what properties it may have.

Overall, the thesis provides both a broad map of phosphosulfides and a set of practical ideas for how new members of this family could be found and evaluated in the future.