The synthesis of lead-free ferroelectric Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 thin films by sol–gel method

(1 − x)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3 [BNT–BKT–100x] thin films have been successfully deposited on Pt/Ti/SiO2/Si substrates by a sol–gel process together with rapid thermal annealing. A morphotropic phase boundary (MPB) between Bi0.5Na0.5TiO3 and Bi0.5K0.5TiO3 was determined around x ∼ 0.15. Near the MPB, the film exhibits the largest grain size, the highest ε value (360) and the largest Pr value (13.8 μC/cm2). The BNT–BKT thin film system is expected to be a new and promising candidate for lead-free piezoelectric applications.