First-principles study of the adsorption of 3d transition metals on BaO- and TiO2-terminated cubic-phase BaTiO3(001) surfaces

The deposition of transition metals (TM) on barium titanate (BaTiO3, BTO) surfaces is involved in the development of several BTO-based devices, such as diodes, catalysts, and multiferroics. Here, we employ density functional theory to investigate the adsorption of 3d TM on both BaO- (type-I) and TiO2-terminated (type-II) surfaces of cubic BaTiO3(001) at low levels of surface coverage, which is important to comprehend the initial stages of the formation and growth of TM overlayers on BTO. The most stable adsorption site is identified for each adatom on both surfaces. Our discussion is based on analyses of structural distortions, Bader charge, electron density difference, magnetic moments, work function, density of states, and adsorption energies. For the type-I surface, most of the adatoms bind covalently on top of the surface oxygens, except for Sc, Ti, and V atoms, which adsorb preferentially on the bridge site, between O ions, to form two polar TM-O bonds. On the type-II surface, the TM are located at the fourfold hollow site, which allows the formation of four TM-O interactions that are predominantly ionic. Upon the adsorption, we noticed the formation of in-gap states originated mostly from the adatom. When electrons are transferred to the substrates, their conduction bands become partially occupied and metallic. We observed a decrease in the work function of the type-II surface that is fairly proportional to the charge gained, which suggests that the BTO work function can be manipulated by the controlled deposition of TM.