Polar topological transitions in PbTiO3 thin films affected by oxygen vacancy content and film thickness

Topological polar textures in ferroelectric films show fundamental physics, intriguing topology, and technological prospects. Understanding the conditions for the emergence of polar topological textures is crucial for future applications. Here, a series of PbTiO3 thin films were grown by pulsed laser deposition via varying the oxygen partial pressure (i.e., oxygen vacancy content) and pulse number (i.e., film thickness). It was found that ∼10-nm-thick films grown at lower oxygen partial pressures exhibit a higher oxygen vacancy content. By decreasing the oxygen partial pressure from 26 to 10 Pa, the as-grown films transition from a downward c-monodomain state to an upward c-monodomain state. Interestingly, at the relatively low oxygen partial pressure of 10 Pa, by further increasing the pulse number from 1500 to 6500, the as-grown films transition from the upward c-monodomain state to a polar skyrmion state, a labyrinth state, and finally a c-domain-dominated state with sparse a-domains. Phase-field simulations indicate that the intricate evolution of polar states mainly arises from the competition between elastic and electrostatic energies modified by the growth conditions. This work should extend our current understanding of the formation mechanism of topological polar states in ferroelectric thin films.