Fabrication of Lead-Free Bi _0.5Na _0.5TiO ₃ Thin Films by Aqueous Chemical Solution Deposition

Abstract

Piezoelectric ceramics are widely used in actuator applications, and currently the vast majority of these devices are based on $\mathrm{Pb}\left(\mathrm{Zr},\mathrm{Ti}\right){\mathrm{O}}_3$ , which constitutes environmental and health hazards due to the toxicity of lead. One of the most promising lead-free material systems for actuators is based on ${\mathrm{Bi}}_{0.5}{\mathrm{Na}}_{0.5}{\mathrm{TiO}}_3$ (BNT), and here we report on successful fabrication of BNT thin films by aqueous chemical solution deposition. The precursor solution used in the synthesis is based on bismuth citrate stabilized by ethanolamine, $\mathrm{NaOH}$ , and a Ti-citrate prepared from titanium tetraisopropoxide and citric acid. BNT thin films were deposited on ${\mathrm{SrTiO}}_3$ and platinized silicon substrates by spin-coating, and the films were pyrolized and annealed by rapid thermal processing. The BNT perovskite phase formed after calcination at 500 °C in air. The deposited thin films were single phase according to X-ray diffraction, and the microstructures of the films shown by electron microscopy were homogeneous and dense. Decomposition of the gel was thoroughly investigated, and the conditions resulting in phase pure materials were identified. This new aqueous deposition route is low cost, robust, and suitable for development of BNT based thin film for actuator applications.