The compensation of the depolarization field in ferroelectric layers requires the presence of a suitable amount of charges able to follow any variation of the ferroelectric polarization. These can be free carriers or charged defects located in the ferroelectric material or free carriers coming from the electrodes. Here we show that a self-doping phenomenon occurs in epitaxial, tetragonal ferroelectric films of Pb(Zr_0.2Ti_0.8)O₃, consisting in generation of point defects (vacancies) acting as donors/acceptors. These are introducing free carriers that partly compensate the depolarization field occurring in the film. It is found that the concentration of the free carriers introduced by self-doping increases with decreasing the thickness of the ferroelectric layer, reaching values of the order of 10²⁶ m⁻³for 10 nm thick films. One the other hand, microscopic investigations show that, for thicknesses higher than 50 nm, the 2O/(Ti+Zr+Pb) atomic ratio increases with the thickness of the layers. These results suggest that the ratio between the oxygen and cation vacancies varies with the thickness of the layer in such a way that the net free carrier density is sufficient to efficiently compensate the depolarization field and to preserve the outward direction of the polarization.

A single ferroelectric Schottky diode was obtained on a SrRuO3-Pb(Zr0.2Ti0.8)O3-Ta (SRO-PZT20/80-Ta) structure in which the SRO-PZT20/80 interface is the rectifying contact and the PZT20/80-Ta interface behaves as a quasiohmic contact. Both the capacitance-voltage (C-V) and the current-voltage (I-V) characteristics show the memory effect due to the ferroelectric polarization. However, retention studies had revealed that only the ``down'' orientation of ferroelectric polarization is stable in time (polarization oriented from top to bottom contact). The analysis of the experimental results suggests that the PZT20/80 is n type and that the stable orientation of polarization is related to the presence of a depletion region at the SRO-PZT20/80 Schottky interface.

Photoelectron spectroscopy studies of (001) oriented PbTi_0.8Zr_0.2O₃ (PZT) single crystal layers with submicron resolution revealed areas with different Pb 5d binding energies, attributed to the different charge and polarization states of the film surface. Two novel effects are evidenced by using intense synchrotron radiation beam experiments: (i) the progressive increase of a low binding energy component for the Pb core levels (evidenced for both 5d and 4f, on two different measurement setups), which can be attributed to a partial decomposition of the PZT film at its surface and promoting the growth of metallic Pb during the photoemission process, with the eventuality of the progressive formation of areas with downwards ferroelectric polarization; (ii) for films annealed in oxygen under clean conditions (in an ultrahigh vacuum installation) a huge shift of the Pb 5d core levels (by 8–9 eV) towards higher binding energies is attributed to the formation of areas with depleted mobile charge carriers, whose surface density is insufficient to screen the depolarization field. This shift is attenuated progressively with time, as the sample is irradiated with high flux soft X-rays. The formation of these areas with strong internal electric field promotes these films as good candidates for photocatalysis and solar cells, since in the operation of these devices the ability to perform charge separation and to avoid electron–hole recombination is crucial.

X-ray photoelectron spectroscopy (XPS) analyses of lead zirco-titanate Pb(Zr,Ti)O₃(001) single crystal thin layers as a function of the time spent between sample preparation by pulsed laser deposition and introduction in to a ultrahigh vacuum revealed the fact that freshly prepared samples showed a shift of the C 1s towards a higher binding energy, together with shifts of core levels originating from the substrate (particularly Ti 2p and O 1s) towards a lower binding energy. This behaviour is explained by considering that the molecules of contaminants (fatty acids, alcohols, esters) are adsorbed preferentially on areas exhibiting outwards polarization P⁽⁺⁾. Thus, photoelectrons originating from contaminants will have larger binding energies because of the charge state of the P⁽⁺⁾ areas, whereas the substrate XPS signals from these P⁽⁺⁾ areas are attenuated by the contaminants, with the consequence of a prevalence of XPS substrate signals originating from the P⁽⁻⁾ areas, shifted towards lower binding energies. Piezoresponse force microscopy confirmed the assumptions derived from XPS results and suggests the existence of an interplay between the adsorption of contaminants and the surface polarization state.