Adsorption of atomic and molecular oxygen on the SrTiO 3 (001) surfaces: Predictions by means of hybrid density function
- PDF / 692,087 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 177 Views
0894-LL08-05.1
Adsorption of atomic and molecular oxygen on the SrTiO3(001) surfaces: Predictions by means of hybrid density functional calculations Sergei Piskunov1,3, Yuri F. Zhukovskii1,3, Eugene A. Kotomin1,3, Eugene Heifets2 and Donald E. Ellis3 1
Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., LV-1063 Riga, LATVIA 2 California Institute of Technology, MS 139-74, Pasadena, CA 91125, USA 3 Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA ABSTRACT Ab initio calculations based on density functional theory (DFT) were used to study the energetics, geometry of fully relaxed structure, and electronic charge redistribution for adsorbed atomic and molecular oxygen on defectless unreconstructed SrTiO3(001) surfaces, both SrO- and TiO2-terminated. B3PW functional used in our calculations contains a ‘‘hybrid’’ of the DFT exchange and correlation functionals with exact non-local Hartree–Fock (HF) exchange. We performed calculations of two-dimensional slabs with unit cells large enough for the adsorbed species to be treated as isolated. We found substantial binding energies for atomic O adsorption at bridge positions between the two adjacent metal and oxygen surface ions (much closer to the latter) on both SrO- and TiO2-terminated surface (over 2.0 eV with respect to free atom). In both cases strong bonding is rather caused by formation of surface molecular peroxide ion in singlet state. For molecular adsorption, different adsorption sites and orientations of O2 molecule were studied, however, adsorption energy never exceeded 0.1 eV. However, energy gain obtained from adsorption of atomic oxygen is not sufficient for molecule dissociation. INTRODUCTION Adsorption of gas-phase oxygen on the ABO3 perovskite surfaces is important for sensors, capacitors, photoelectrodes, in photocatalysis, and for fuel cell applications [1,2]. The difficulties with distinguishing between adsorbed and lattice oxygen (unless the adsorbed species carry a net spin) result in a significant lack of experimental information about the oxygen adsorption processes occurring on perovskite surfaces. Furthermore, the results of ab initio simulations of oxygen adsorption on ABO3 perovskites are very scarce in the literature. Very little is known even on the adsorption mechanisms of oxygen atoms/molecules on oxide surfaces: to the best of our knowledge, up to now careful first-principles calculations were performed only for simplest MgO and SnO2 oxides [3,4]. In this paper, we report the results of large-scale ab initio calculations which have been performed to shed light on the processes occurring during adsorption of atomic and molecular oxygen on the defect-free cubic SrTiO3(001) surfaces. (Due to its simplicity, the cubic SrTiO3, stable at room temperatures [5], is an excellent model material for a study of chemistry processes occurring at perovskite surfaces.) At the same time, since Ti-rich terminations of SrTiO3 undergo extensive reconstruction under high vacuum conditions, it is not clea
