Tailoring preferential orientation in BaTiO3-based thin films from aqueous chemical solution deposition

Abstract

Ferroelectric properties of thin films can be enhanced by crystallographic texture. In this work, we report on how heat treatment of films can be designed to tailor the degree of preferential orientation in BaTiO3-based thin films from aqueous chemical solution deposition. In situ synchrotron X-ray diffraction in combination with Rietveld refinements was used to study the crystallization process of films from a single deposition and to give an in depth characterization of the crystallographic texture of the films. Transmission electron microscopy was employed to evaluate the microstructure and degree of preferred orientation in thicker films from multiple depositions. Texture was induced in the multilayer films by a repeated annealing process. Cube-on-cube growth was demonstrated to occur in both single and multi-layered films provided the heating program was designed to give limited nucleation and growth below the threshold for where cube-on-cube growth is favoured, resulting in a very high degree of preferred orientation. The cube-on-cube grown films were relaxed with respect to the lattice unit cell mismatch between the film and the substrate, where strain and relaxation depend on the film thickness. Texture and cube-on-cube growth were demonstrated on several types of single crystal substrates. Calcium and zirconium substitution did not alter the crystallization process, but zirconium decreased the texture formation kinetics. The ferroelectric response was strongest in the films with a high degree of preferred orientation.