Evolution of a₁/a₂ Domains in Strained Ferroelectric Thin Films

Ferroelectric domains are of great importance in both scientific and application aspects ^[1]. Tailoring their novel configurations and understanding their structural evolution are crucial to better controlling the domain configurations for future devices. We grow ferroelectric PbTiO₃ films with various thicknesses on scandate substrates by Pulsed Laser Deposition (PLD) technique. By means of Cs-corrected Transmission Electron Microscopy (TEM) , the domain structures were characterized in PbTiO₃ thin films. It is found that PbTiO₃ films grown on SmScO₃ substrates are domain oriented consisting of dominant a₁/a₂ domains. The a₁/a₂ domains distribute periodically and the width increases with increasing film thickness. Further increasing film thickness, a/c domains appear. The critical thickness for the formation of a₁/a₂ domains is around 2 nm. Cs-corrected STEM imaging demonstrates that the domain walls of a₁/a₂ domain structure have the rotation characteristic of 90° ferroelastic domain wall.