Microwave losses in incipient ferroelectrics as functions of the temperature and the biasing field

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. (C) 1998 American Institute of Physics. [S0021-8979(98)00614-8].