Electronic properties and surface reactivity of SrO-terminated SrTiO₃ and SrO-terminated iron-doped SrTiO₃

Abstract

Surface reactivity and near-surface electronic properties of SrO-terminated SrTiO3 and iron doped SrTiO3 were studied with first principle methods. We have investigated the density of states (DOS) of bulk SrTiO3 and compared it to DOS of iron-doped SrTiO3 with different oxidation states of iron corresponding to varying oxygen vacancy content within the bulk material. The obtained bulk DOS was compared to near-surface DOS, i.e. surface states, for both SrO-terminated surface of SrTiO3 and iron-doped SrTiO3. Electron density plots and electron density distribution through the entire slab models were investigated in order to understand the origin of surface electrons that can participate in oxygen reduction reaction. Furthermore, we have compared oxygen reduction reactions at elevated temperatures for SrO surfaces with and without oxygen vacancies. Our calculations demonstrate that the conduction band, which is formed mainly by the d-states of Ti, and Fe-induced states within the band gap of SrTiO3, are accessible only on TiO2 terminated SrTiO3 surface while the SrO-terminated surface introduces a tunneling barrier for the electrons populating the conductance band. First principle molecular dynamics demonstrated that at elevated temperatures the surface oxygen vacancies are essential for the oxygen reduction reaction.

Examining the surface evolution of LaTiOxNy an oxynitride solar water splitting photocatalyst

“…of these oxides and oxynitrides tend to show AO (La-O) termination rather than BO 2 (TiO 2 ) surface terminations 24,[33][34][35] . The La cations are much larger than Ti (1.03−1.16 Å and 0.61 −0.67 Å respectively) and so the surface would consist primarily of La-O atoms where the Ti B cations sink down slightly into the sub-surface layers, which could explain why the A site shows evidence to be the catalytically active site for the OER.…”

Interaction of SrO-terminated SrTiO3 surface with oxygen, carbon dioxide, and water

“…The oxide lattice. 20,23 In this work we investigate the interaction of molecular water with a surface oxygen vacancy site. The results are summarized in Figure 5.…”

“…our previous calculations which include both DFT and DFT-MD simulations 20,23. Our previous results demonstrate that oxygen vacancies are stabilized within the SrO surface layer ofSrTiO 3 .…”

“…For example, iron doping in SrTiO 3 lattice can lead to elimination of one oxide ion per two Fe 3+ ions in the lattice. 20 Doping can be performed either on the A-sites, B-sites, or both, A-and B-sites, and can lead to perovskite materials with complicated chemical composition and various tunable properties such as electronic conductivity, ionic conductivity, or surface exchange.…”

“…24 The electronic properties in the vicinity of surface oxygen vacancies of SrTiO 3 have shown that those vacancies are not simply spatial voids but are regions in space characterized with high electron density. 20 As the molecular oxygen activation and dissociation in an electrophilic reaction, surface oxygen vacancies would be the preferred surface active sites. The oxygen vacancies in SrTiO 3 have been found to be slightly stabilized within the SrO surface layer compared to the subsurface TiO 2 layer.…”