The main interest in the area of practical applications of ferroelectrics, particularly at the microwave frequency, is oriented now to room temperature. In this connection, ferroelectrics like BaxSr1−xTiO3 should be carefully studied. Such materials are characterized by the second order phase transition. In a perfect ferroelectric crystal, the phase transition takes place at temperature TC, which is called the Curie temperature. Real (defected) crystals and ceramic samples are characterized by a presence of built-in electric field and mechanical strains. In the case of the real crystal, the temperature of the phase transition TC′, is displaced to lower temperature and the temperature of the maximum of ε(T)Tm is displaced to higher value with respect to TC. Thus, for the real ferroelectric sample (not for an incipient ferroelectric), one has TC′<TC<Tm. Some investigators suppose by default that TC′=TC=Tm. Such a supposition is wrong and can lead to an incorrect treatment of experimental results. In the case of a thin film sample, the phase transition and the dielectric response of a ferroelectric sample are affected by the size of the sample, what is treated as a size effect. Experimental data obtained as a result of measurement of the dielectric constant as a function of temperature can be used for finding the Curie temperature and other parameters of the material. For this procedure, a suitable model of the dielectric response of the ferroelectric sample should be used.

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The dielectric constant of ferroelectric materials can be controlled by an applied electric field. That is promising for applications using the microwave technique. The widespread use of ferroelectric materials at microwaves is retarded by a considerable high dielectric loss by the materials at high frequencies. The goal of this article is to model the essential mechanisms of losses in incipient ferroelectrics at microwave frequencies. The following materials are studied: strontium titanate (SrTiO3) and potassium tantalate (KTaO3). The following loss mechanisms are considered: fundamental loss determined by multiphonon scattering of the soft ferroelectric mode and transformation of microwave electric field oscillations into acoustic oscillations due to residual ferroelectric polarization.

Interest in incipient ferroelectrics has been renewed due to their promise for applications at cryogenic temperatures. The dependence of the dielectric constant of an incipient ferroelectric on temperature and the applied biasing field can be modeled correctly by solution of the Ginsburg–Devonshire equation. A set of simple and correct formulas is derived to provide simulation of the dielectric constant of an incipient ferroelectric as a function of temperature and the biasing field. As a typical representative of this, SrTiO3 is used. The inhomogeniety of the composition or/and structure of the material is quantitatively described by a specially introduced coefficient. The correlation effect is used to describe the size effect for a thin film capacitor. The boundary conditions for a ferroelectric polarization on the surface of electrodes are considered. The boundary conditions are specified for the interface between the ferroelectric and the metal or the high temperature superconductor. Comparison of the simulated and experimental data for both the bulk sample and for the thin film capacitor shows good numerical agreement. The model is intended to be used for developing the computer aided design of microwave components and devices based on ferroelectric films.

Ferroelectricity in sol-gel derived Ba 0.8 Sr 0.2 TiO 3 thin films using a highly diluted precursor solution