Richard, Adrien; (2024) A Computational Study of the Wadsley-Roth Family and Related Energy Materials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The research and development of new materials with functional behaviours and properties towards energy uses is a complex endeavour require precise methods and a good understanding of the underlying chemistry of these materials. Due to the increasing complexity and sustainable requirements for new materials, traditional experimental techniques need to be paired with computational modelling techniques. This thesis describes two of the main facets of improved computational modelling. The first part of this thesis discusses the use of the sol-3c methods, novel adaptations of existing functionals and basis sets through the addition of semi-empirical corrections. I apply them to transition metal oxides, notably four polymorphs of TiO2. The analysis of precision and computational expenses allowed us to determine whether these methods represent an improvement on existing methods. To be considered improvements, these methods need to be faster and more precise. Further investigating the use of semi-empirical corrections for better transition metal oxide property prediction, I use dispersion-corrected versions of existing functionals applied to polymorphs of TiO2, MnO2 and ZnO. The inclusion of dispersion interactions in these calculations allows us to reproduce experimental orderings of polymorphic stability and informs on the relevance of these interactions for the relative stability of polymorphic phases. In the second part of this thesis, I investigate the relationship between structure and electronic properties in the Wadsley-Roth materials family for energy uses, notably as electrodes. Despite being increasingly studied in published work, the underlying chemistry of these materials is relatively unknown since their original discovery in the 1960’s. Current research focuses on single compositions of these materials and rarely considers properties across the materials family. The bottom-up study of this family of transition metal oxides formed from crystallographic shear planes based on titanium, tungsten and niobium serves as a basis of understanding for the chemistry governing these materials and their particular ReO3-type block structure. This study was completed using a high level of computational accuracy starting from the most basic properties of the pure phases to the activation of their functional behaviour, which reveals the mechanisms governing these materials and provides insights that are unobtainable using a lower level of theory or solely experimental methods.

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