Dielectric Response of Soft Modes in Ferroelectric Thin Films

Abstract

The concept of effective soft mode in thin films and its role in the effective dielectric response of high-permittivity thin films is introduced. Compared to bulk soft mode response, it may be strongly influenced by stresses from the substrate and dielectric inhomogeneities like interface layers, grain boundaries and porosity. The available techniques for the determination of the effective soft-mode response (far-infrared and time-domain THz spectroscopies) are discussed. The experiments on various ferroelectric (PbTiO 3, PZT, BaTiO 3, SrBi 2 Ta 2 O 9 ), incipient ferroelectric (SrTiO 3 ), doped incipient ferroelectric (SrTiO 3 :Ba), and relaxor ferroelectric (PLZT) films are briefly reviewed and compared with the results in bulk materials.