Polarization in pseudocubic epitaxial relaxed PMN-PT thin films

Abstract

Understanding the relationship between structural characteristics and functional properties of complex relaxor ferroelectric thin films is of high interest for designing materials with high performances. In this work, the structure of epitaxial relaxed pulsed-laser-deposited Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT; x 25, 33, and 40) thin films on LaNiO3/SrTiO3 substrates is analyzed using a variety of diffraction and spectroscopic techniques. While based on the data obtained from high-resolution x-ray diffraction and scanning transmission electron microscopy analysis, the average structure of the PMN-xPT films is metrically cubic, micro-Raman polarimetry measurements indicate the tetragonal-like ferroelectric phase with marked preference for the polarization perpendicular to the film for all three compositions. The results of the Raman scattering analysis are supported by electromechanical properties of the samples, which clearly show that the films have a locally non-centrosymmetric structure. Furthermore, only a gradual enhancement of the electrical properties from PMN-25PT to PMN-40PT is observed, which is attributed to small tetragonal distortions that are highly similar for all three compositions.