Euler ferroelectrics

Subsequently we consida" epitaxial monodomain ferroelectric films. The material is supposed to have perovskite structure and is a perfect insulator. In this case the depolarization field can be diminished under the influence of electrodes only. For the case of superconducting electrodes the depolarization field of such film had been calculated in Ref. [12], where it has been shown that Ef = 4n (P — P ) (P is the average polarization). Substituting this expression into (3.10a) and performing variation, one obtains following Euler-Lagrange equation for Pj(zy. 

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