Influence of semiconducting electrodes on properties of thin ferroelectric films

The influence of semiconducting electrodes on the properties of thin ferroelectric films is considered within the framework of the phenomenological Ginzburg-Landau theory. The contribution of the electric field produced by charges in the electrodes allowing for the screening length of the carriers is included in the functional of the free energy and so in the Euler-Lagrange equation for the film's polarization. Application of the variational method to the solution of this equation allows the transformation of the free energy functional into a conventional type of free energy with renormalized coefficients. The obtained dependence of the coefficients on the film thickness, temperature, electrodes, carrier screening length, and other parameters make it possible to calculate the dependence of the properties on these parameters by conventional minimization of the free energy. The semiconducting carrier screening length was shown to influence strongly the film's properties and critical parameters of the thickness-induced phase transition. At some fixed temperature and thickness of the film electrode an induced phase transition from the ferroelectric to the paraelectric phase is shown to exist when the screening length of the carriers is larger than some critical value. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.