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Defect-driven flexochemical coupling in thin ferroelectric films

Eliseev, Eugene A. and Vorotiahin, Ivan S. and Fomichov, Yevhen M. and Glinchuk, Maya D. and Kalinin, Sergei V. and Genenko, Yuri A. and Morozovska, Anna N. (2018):
Defect-driven flexochemical coupling in thin ferroelectric films.
In: Physical Review B, pp. 024102(17), 97, (2), ISSN 2469-9950,
DOI: 10.1103/PhysRevB.97.024102,
[Online-Edition: https://doi.org/10.1103/PhysRevB.97.024102],
[Article]

Abstract

Using the Landau-Ginzburg-Devonshire theory, we considered the impact of the flexoelectrochemical coupling on the size effects in polar properties and phase transitions of thin ferroelectric films with a layer of elastic defects. We investigated a typical case, when defects fill a thin layer below the top film surface with a constant concentration creating an additional gradient of elastic fields. The defective surface of the film is not covered with an electrode, but instead with an ultrathin layer of ambient screening charges, characterized by a surface screening length. Obtained results revealed an unexpectedly strong effect of the joint action of Vegard stresses and flexoelectric effect (shortly flexochemical coupling) on the ferroelectric transition temperature, distribution of the spontaneous polarization and elastic fields, domain wall structure and period in thin PbTiO3 films containing a layer of elastic defects. A nontrivial result is the persistence of ferroelectricity at film thicknesses below 4 nm, temperatures lower than 350 K, and relatively high surface screening length (∼0.1nm). The origin of this phenomenon is the flexoelectric coupling leading to the rebuilding of the domain structure in the film (namely the cross-over from c-domain stripes to a-type closure domains) when its thickness decreases below 4 nm. The ferroelectricity persistence is facilitated by negative Vegard effect. For positive Vegard effect, thicker films exhibit the appearance of pronounced maxima on the thickness dependence of the transition temperature, whose position and height can be controlled by the defect type and concentration. The revealed features may have important implications for miniaturization of ferroelectric-based devices.

Item Type: Article
Erschienen: 2018
Creators: Eliseev, Eugene A. and Vorotiahin, Ivan S. and Fomichov, Yevhen M. and Glinchuk, Maya D. and Kalinin, Sergei V. and Genenko, Yuri A. and Morozovska, Anna N.
Title: Defect-driven flexochemical coupling in thin ferroelectric films
Language: English
Abstract:

Using the Landau-Ginzburg-Devonshire theory, we considered the impact of the flexoelectrochemical coupling on the size effects in polar properties and phase transitions of thin ferroelectric films with a layer of elastic defects. We investigated a typical case, when defects fill a thin layer below the top film surface with a constant concentration creating an additional gradient of elastic fields. The defective surface of the film is not covered with an electrode, but instead with an ultrathin layer of ambient screening charges, characterized by a surface screening length. Obtained results revealed an unexpectedly strong effect of the joint action of Vegard stresses and flexoelectric effect (shortly flexochemical coupling) on the ferroelectric transition temperature, distribution of the spontaneous polarization and elastic fields, domain wall structure and period in thin PbTiO3 films containing a layer of elastic defects. A nontrivial result is the persistence of ferroelectricity at film thicknesses below 4 nm, temperatures lower than 350 K, and relatively high surface screening length (∼0.1nm). The origin of this phenomenon is the flexoelectric coupling leading to the rebuilding of the domain structure in the film (namely the cross-over from c-domain stripes to a-type closure domains) when its thickness decreases below 4 nm. The ferroelectricity persistence is facilitated by negative Vegard effect. For positive Vegard effect, thicker films exhibit the appearance of pronounced maxima on the thickness dependence of the transition temperature, whose position and height can be controlled by the defect type and concentration. The revealed features may have important implications for miniaturization of ferroelectric-based devices.

Journal or Publication Title: Physical Review B
Volume: 97
Number: 2
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 30 Jan 2018 09:27
DOI: 10.1103/PhysRevB.97.024102
Official URL: https://doi.org/10.1103/PhysRevB.97.024102
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