Infrared activity in the Aurivillius layered ferroelectric

Abstract

Experimental studies were carried out on infrared-active phonons in the Aurivillius ferroelectric (Formula presented) (SBT), using reflectivity measurements (down to (Formula presented)) and transmission measurements (down to (Formula presented)) on crystals, pellets, and thin films. An analysis was done of the contrasting consequences of the competing orthorhombic and pseudotetragonal symmetries in SBT. Reflectivity results for light polarized in the (Formula presented) plane show that the anisotropy in this plane is small in the frequency range from 300 to (Formula presented) indicating the influence of the approximate tetragonal symmetry. Dielectric dispersion properties were derived for this polarization (Formula presented) in this frequency range. The transverse-optical (TO) and longitudinal-optical (LO) frequencies corresponding to the dominant (Formula presented) band are 613 and (Formula presented) respectively. This strong, high-frequency band arises from a mode dominated by the motion of the oxygen sublattice; its TO and LO frequencies yield an oxygen-ion Szigeti effective charge of (Formula presented) Frequency estimates for the TO (LO) pairs of other strong bands are 188(330) and (Formula presented) for (Formula presented) and 610(675) and (Formula presented) for (Formula presented) In addition to the main infrared bands, the main Raman bands of SBT are also reported. © 1998 The American Physical Society.