Oxygen Deficiencies in Titanium Oxide Clusters as Models for Bulk Defects

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2022-01, Vol.126 (2), p.211-220
• Main Authors: Heald, Lauren F, Garcia, Jacob M, Sayres, Scott G
• Format: Article
• Language: English
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.1c07733

TD-DFT calculations were performed on neutral Ti n O2n , Ti n O2n–1, and Ti n O2n–2 clusters, where n ≤ 7. Calculations show the Ti n O2n clusters are closed shell systems containing empty d orbitals and that the partially filled d orbitals of the suboxide clusters have a profound effect on their structural, electronic, and topological properties. The low energy photoexcitations of Ti n O2n clusters are all O-2p to Ti-3d transitions, while the open-shell suboxide clusters are all characterized by d–d transitions that occur at a much smaller optical gap. Upon low energy photoabsorption, the localization of the hole is accompanied by a local bond elongation, i.e., polaron formation, whereas d-electrons are generally delocalized around the cluster. The properties of the clusters, including the oxygen binding energies and structures, were calculated to account for the variation in relative populations found in experimental cluster distributions. Several Ti n O2n–2 clusters contain higher symmetry which is reflected in their relative stability. In particular, the tetrahedral symmetry of Ti4O6 inhibits charge carrier localization and therefore exhibits higher stability.