Influence of ferroelectric polarization on the equilibrium stoichiometry of lithium niobate (0001) surfaces.

We present a first-principles density functional theory study predicting the relative thermodynamic stability of ferroelectric lithium niobate (LiNbO3) (0001) surfaces of different stoichiometry. We predict that the equilibrium stoichiometries are different for the positively and negatively polarized LiNbO3 surfaces under the same conditions. Based on the modern theory of polarization, we demonstrate how a simple ionic model can be used to calculate surface charges for ferroelectric surfaces with intrinsic polar stacking. It is found that surface charge passivation by ions is thermodynamically favored over passivation by mobile carriers in a wide range of chemical potentials.