It is known that the permittivity of the ferroelectric films is affected byseveral phenomena, which deteriorate the material quality (e.g. theredistribution of the crystal lattice defects, appearance of theelectrode-adjacent non-ferroelectric layers or the spontaneous polarizationscreening due to a free charge injection across the electrode-adjacent layer,etc.). It is also known that the permittivity of ferroelectric polydomain filmsis controlled by the sum of two contributions: the crystal lattice (intrinsic)contribution and the domain wall movement (extrinsic) contribution. It is thelatter one, which is very sensitive to the aforementioned phenomena and whichplays a key role in the deterioration of the dielectric response of theferroelectric polydomain films. In this Article, there is presented a methodfor the identification of the process, which is responsible for theferroelectric ageing. The method is based on the analysis of the evolution ofboth the linear and nonlinear permittivity during ageing. Applicability of themethod is theoretically demonstrated on four ageing scenarios in twoqualitatively different systems where the evolution of the nonlinearpermittivity is controlled, first, by a redistribution of the pinning centerson the domain wall and, second, by microstructural changes at the interfacebetween the ferroelectric layer and the electrode. It is shown that each ageingscenario is characterized by unique trend in the evolution between the linearand nonlinear part of the permittivity, which can be verified experimentally.
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