Ferroelectricity and tetragonality in ultrathin PbTiO3 films

TL;DR

This study investigates how the ferroelectric properties and tetragonality of ultrathin PbTiO3 films change with decreasing thickness, revealing a reduction in polarization but retention of ferroelectricity even at very small scales.

Contribution

It combines high-resolution x-ray measurements with a first-principles model to elucidate the relationship between film thickness, tetragonality, and polarization in ultrathin PbTiO3 films.

Findings

Tetragonality decreases systematically below 200 Å.

Polarization reduces significantly below 50 Å but remains ferroelectric.

Residual depolarizing fields influence polarization in ultrathin films.

Abstract

The evolution of tetragonality with thickness has been probed in epitaxial c-axis oriented PbTiO3 films with thicknesses ranging from 500 down to 24 Angstroms. High resolution x-ray pointed out a systematic decrease of the c-axis lattice parameter with decreasing film thickness below 200 Angstroms. Using a first-principles model Hamiltonian approach, the decrease in tetragonality is related to a reduction of the polarization attributed to the presence of a residual unscreened depolarizing field. It is shown that films below 50 Angstroms display a significantly reduced polarization but still remain ferroelectric.