Study by high resolution electron microscopy and electron diffraction of the La0.03Sr0.255Ba0.7Nb2−yTiyO6−y/2 ferroelectric ceramic

Abstract

The stoichiometric La0.03Sr0.255Ba0.7Nb2−yTiyO6−y/2 (LSBNT) ceramic system was obtained for three different concentrations of titanium ions (y=1%, 3%, and 5%) where the Nb5+ was substituted by Ti4+ according to the expression La0.03Sr0.255Ba0.7Nb2−yTiyO6−y/2. The incommensurate modulation in the LSBNT structure has been studied by high-resolution transmission electron microscopy (HRTEM) and electron diffraction. The location of the incommensurate superlattice spots in the tetragonal phase through the [110] zone in the electron diffraction patterns was measured to determine the incomensuration parameter δ. Structural modulation was also evident by HRTEM for the [001] zone, where a sinusoidal variation along [110] and [11̄0] was identified in coincidence with the electron diffraction patterns. Random occupation of the crystallographic sites that promotes structural variations may be the cause for structural incommensuration. It was possible to identify directly the tetragonal tungsten bronze structure and the presence of point defects that influence the dielectric properties.