Thickness Induced Ferroelectricity in Antiferroelectric Thin Films

4 Thickness Induced Ferroelectricity in Antiferroelectric Thin Films 

This section can be regarded as continuation of previous Sect. 3.2.3 devoted to built-in field influence on the films properties. On the other hand, the antiferroelectrics 

The existence of ferroelectric phase in sufficiently thin antiferroelectric films had been revealed experimentally in several works [64-66]. In Ref. [64], the switchable ferroelectric polarization has been observed in PbZrOs antiferroelectric thin film on Si substrate. It has been revealed, that both in the latter film and in one more antiferroelectric BiNb04 one, the ferroelectric phase appears only if the film thickness is smaller then certain threshold value, which depends on material parameters. For instance, the ferroelectric hysteresis loop has been observed [65] in 100 nm thick PbZrOs/Si Alms, while those thicker than 400-500 nm revealed antiferroelectric behavior. Note, that the other primary ferroic demonstrates the same behavior. Namely, the films of antiferromagnetic BiFeOs on SrTiOs substrate reveal the emergence of ferromagnetism at the thicknesses less than 100 nm [67]. 

3 Theoretical Description of Primary Nanofetroics. Comparison of the Theory... 

The calculations physical properties of antiferroelectrics based on the Kittel model (i.e. with respect to antiparallel alignment of sublattices polarization vectors) can be done within the formalism of Chap. 1. The numerical calculations of phase diagrams of nanosized antiferroelectric systems of different shapes were carried out in Ref. [68] without consideration of either external or internal electric fields. Corresponding analytical calculations had been carried out in Ref. [69], However, the model used for calculations in [69] did not take into account both mechanical strains and surface piezoeffect generating built-in field. The consistent account for latter effects in Ref. [70] show that they are playing a decisive role in transformation of antiferroelectric phase into ferroelectric one in sufficiently thin Aims. With respect to the latter, the subsequent consideration will be done according to Ref. [70]. 

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