In ferroelectric materials, the structure and stability of domains with different polarisation depends crucially on both external boundary conditions and internal defects which together determine the screening of depolarising fields, nucleation thresholds, and domain wall pinning. Here, we explore their combined effects on polarisation orientation, switching dynamics, domain wall roughness, and domain wall conduction, using scanned probe microscopy and structural characterisation of epitaxial ferroelectric thin films and heterostructures under different relative humidity, ultrahigh vacuum, and with different defect densities.

In PbTiO3 thin films we show a reversal of the intrinsic polarisation orientation and the sign of the imprint as a function of growth temperature, under varying electrostatic screening, and relate the observed effects to oxygen vacancy gradients. In Pb(Zr0.2Ti0.8)O3 thin films, we show slow growth and significantly increased roughening of domains when decreasing relative humidity and increasing oxygen vacancy density. We numerically probe the relative contributions of surface adsorbates and disorder, in good agreement with the experimental observations. Using a “pump-probe” approach we also explore the earliest stages of domain switching, demonstrating an unexpectedly long term (over 100 ms) metastability of the (sub)critical nucleus formed under very short repeated bias pulses at the probe tip. We combine these observations with parallel conductive-tip atomic force microscopy current measurements, which show highly localised variations in conductance, and highlight the key role played by oxygen vacancies and surface adsorbates, whose redistribution allows the reversible transition between insulating and conducting transport behaviour at the domain walls.