Ink-jet printed BNT thin films with improved ferroelectric properties via annealing in wet air

In this work, an ink-jet printing process based on the sol-gel route was applied to prepare lead-free ferroelectric Na_0.5Bi_0.5TiO₃(BNT) thin films for the first time. Dense and crack-free films with perovskite structure were obtained from a modified precursor solution through multiple printing and pyrolysis processes. The ferroelectric, dielectric and electrical properties were significantly affected by the annealing temperature and atmosphere. The film annealed at 670?°C in wet air showed a high remnant polarization of 24.7?μC/cm² with a low coercive field of 263?kV/cm, the dielectric constant and loss were 185 and 0.1 at 10?kHz, respectively. It was found that wet air was an alternative to reduce oxygen vacancies and enhance properties of ferroelectric films, which can be explained by the defect chemical reaction between water and oxygen vacancies. X-ray photoelectron spectroscopy(XPS) confirmed the decrease of oxygen vacancies after annealing with water presence, with a formation of Ohmic conduction mechanism dominated by charged hydroxyl groups.