Revealing the phase transition scenario in antiferroelectric thin films by x-ray diffuse scattering

Abstract

There is no consensus among researchers regarding how phase transitions occur in antiferroelectric (AFE) epitaxial heterostructures, in particular, in heterostructures based on model AFE lead zirconate. The questions about the number of phase transitions in such films and by what mechanism they occur remain controversial. This paper presents a look at the phase transition scenario in two types of epitaxial heterostructures: PbZrO3/Ba[La–Sn]O3/MgO (001) thin films with thicknesses from 25 to 1000 nm and PbZrO3/SrRuO3/SrTiO3 (001) thin film 100 nm thick using the diffuse x-ray scattering in the grazing incidence setup. We register the characteristic butterfly-shaped diffuse scattering (DS) intensity distribution in the HK pseudocubic planes, which corresponds to the anisotropic ferroelectric soft mode. No incommensurate soft mode was observed in the cuts of reciprocal space parallel to the film surface by diffuse scattering. We reproduce the shape of DS distribution at different temperatures by the model based on the dielectric stiffness and the electric polarization correlation tensor in the cubic approximation. Such modeling allows not only to characterize the DS parameters from the challengingly low signal-to-background data set, but also to extract experimentally the sensitivity of the materials with respect to inhomogeneous polarization. While the observed temperature evolution of DS is consistent with the dielectric measurements, the correlation between the DS and the phase transition sequence observed by superstructure reflections is yet to be understood better.