Modeling of The Tunability Properties and Switching Properties in Ferroelectric Ceramics with Different Grain Sizes

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Abstract
08-051 Leontin Padurariu Padurariu, L.(Al. I. Cuza University of Iasi); Curecheriu, L.(Alexandru Ioan Cuza University); Ciomaga, C.(Al. I. Cuza University of Iasi); MITOSERIU, L.(Al. I. Cuza University of Iasi); The role of grain size on the tunability (electric field dependence of the dielectric constant) and the switching properties (polarization dependence on the applied field) in ferroelectric ceramics with various grain sizes was studied by an experimental-modeling approach. The model represents an innovative combination between Finite Element Method and Monte Carlo simulations. The Finite Element Method (based on Maxwell equation) was used to describe the inhomogeneity of the local electric field introduced by grain boundaries (characterized by lower permittivity than the grain bulk) and the polarization variation within the Monte Carlo discretization grid (the role of domain structure). Therefore, Finite Element Method was employed to describe the electric interaction between local dipoles and the depolarizing effects. The Monte Carlo simulations (based on Landau-Ginzburg-Devonshire theory) were used to describe the domain structure formation and evolution under field. The simulation results were compared with barium titanate ceramics with grain sizes from few µm to 100 nm. A remarkable agreement between the experimental tunability data and the simulation results was obtained: (i) the linearization of the permittivity dependence on the applied electric, (ii) the reduction of the effective permittivity and the tunability when reducing grain size. The simulations showed, also, a very good agreement between the predicted switching properties and the experimental results when reducing grain size: (i) the increase of the coercive field and the tilting degree of the polarization dependence on the applied field (hysteresis loop), (ii)the reduction of the saturation/remanent polarization and hysteresis area. 
Acknowledgements: This work was supported by the CNCS-UEFISCDI Project No. PN-III-P1-1.1-2016-2016-1069
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