Density functional study of PbTiO3 nanocapacitors with Pt and Au electrodes

We present an ab initio density functional study of ferroelectricity in single-domain PbTiO3-based nanocapacitors. We used density functional theory with the recently introduced PBEsol generalized-gradient exchange-correlation functional, which we found to give accurate properties of bulk ferroelectric (FE) materials. Pt and Au electrodes are used in our study to gain a thorough understanding of the electrode-oxide interfaces, and the role of the interfacial chemical bonding and charge transfer in stabilizing the FE polar phase. We found that the FE properties of the thin films depend not only on the electrode and the FE material but also on the electrode-perovskite termination (TiO2 vs PbO), exemplifying the key role of the interface in these systems. The critical thickness was found to be 24-28 angstrom. In addition, a Lowdin orbital analysis gives a detailed description of the distribution of charges in the system, and shows the importance of charge passivation by the electrodes in stabilizing the FE polar phase.