Strong reciprocal interaction between polarization and surface stoichiometry in oxide ferroelectrics.

We present a systematic evaluation of the effects of polarization switchability on surface structure and stoichiometry in BaTiO3 and PbTiO3 ferroelectric oxides. We show that charge passivation, mostly by ionic surface reconstructions, is the driving force for the stability of the surfaces, which suggests that varying the substrate polarization offers a new mechanism for controlling surface reconstructions in polar systems and inducing highly nonstoichiometric structures. Conversely, for thin-films the chemical environment can drive polarization switching via induced compositional changes on the surface. We find that the value of the oxygen partial pressure for the positive-to-negative polar transition is in good agreement with the recent experimental value for thin-film PbTiO3. For BaTiO3, we show that it is harder for oxygen control to drive polar transition because it is more difficult to reduce. This study opens up the possibility of real-time control of structure and composition of oxide surfaces.