Preparation and ferroelectric properties of K_0.5Na _0.5NbO₃ thin films derived from non-alcohol niobium salt sol-gel process

Lead-free K_0.5Na_0.5NbO₃ (KNN) thin films were prepared on Pt (111) /Ti/SiO₂/Si (100) substrates by a polyvinylpyrrolidone (PVP)-modified sol-gel method without any metal alkoxides. The effects of PVP on the crystallization, surface morphology and electrical properties were investigated. It was found that the introduction of PVP into the sol could reduce the annealing temperature, enhance the surface quality and improve the KNN film of (100) oriented growth. Compared with the pure non-PVP-modified KNN thin films, the dielectric and ferroelectric properties of the KNN films were significantly enhanced by adding PVP into the sol. In particular, the PVP-modified KNN films which were annealed at 550°C exhibited relatively saturated polarization-electric field (P-E) hysteresis loops with high remnant polarization P_r of 22 C/cm², dielectric constant of 280 and dielectric loss of 0.09, respectively, indicating promising lead-free piezoelectric film candidate for future applications.