The evolution of polarization inside ultrathin PbTiO₃ films: a theoretical study

Abstract

How to control the material properties by manipulating the unitcell thickness is crucial for applications of ferroelectric ultrathin films. To understand the polarization behaviour of ultrathin PbTiO₃ (PTO) films grown on SrTiO₃ (STO) substrate, we have systematically explored the strength and direction of polarization in each unitcell layer, using density functional theory combined with Born effective charge method. Strikingly, we find that the polar state of ultrathin PTO films is a composite result depending not only on thickness but also on boundary condition, initial polarization direction, etc. Besides, we also studied the surface effect on the polarization in the thicker PTO films for comparison with the ultrathin ones, which suggests that the surface effect is basically confined in a small range (3–5 unitcells thick at surface region) no matter what kinds of surface terminations and polarization directions.

Keywords:

• ultrathin films
• first-principles calculation
• polarization

Acknowledgement

We acknowledge National Supercomputing Center in Shenzhen (China) for providing the computational resources.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work is supported by the National Natural Science Foundation of China [grant number 51231007], [grant number 51171190], [grant number 51371176], [grant number 51401212]; the National Basic Research Program of China [grant number 2014CB921002].