Crystal defects and cation ordering domains in epitaxial PbSc 0.5Ta 0.5O 3 relaxor ferroelectric thin films investigated by high -resolution transmission electron microscopy

Abstract

Epitaxial thin films of the relaxor ferroelectric PbSc 0.5Ta 0.5O 3 (PST) were grown by pulsed laser deposition on an SrTiO 3 substrate with an SrRuO 3 buffer layer and investigated by diffraction contrast imaging and high-resolution transmission electron microscopy (TEM) in cross-section and plan-view. Crystal defects, viz. misfit dislocations, π stacking faults and cation ordering domains, have been characterized and the mechanism of their formation is discussed. The state of the structural disorder in PST relaxor thin films is characterized by the high density of π stacking faults and the rather small size (<10 nm) of the cation ordering domains, and is therefore markedly distinct from the state of the disorder in bulk relaxor PST. Polar nanoregions, supposed to be essential for explaining the relaxor properties, could not be detected using TEM, possibly due to their high fluctuation frequency. The dielectric constant of the relaxor PST thin films is about an order of magnitude smaller than that of bulk relaxor PST, which is attributed to the large density of π stacking faults in the thin films.