Effects of thickness on structures and electrical properties of K _0.5Na _0.5NbO ₃ thick films derived from polyvinylpyrrolidone-modified chemical solution

Lead-free ferroelectric K _0.5Na _0.5NbO ₃ (KNN) films with different thicknesses were prepared by polyvinylpyrrolidone (PVP)-modified chemical solution deposition (CSD) method. The KNN films with thickness up to 4.9 μm were obtained by repeating deposition-heating process. All KNN thick films exhibit single perovskite phase and stronger (1 1 0) peak when annealed at 650°C. The variation of dielectric constant with thickness indicates that there exists a critical thickness for the dielectric constant in the KNN films which should lie in 1.3-2.5 μm. The similar trend is observed for the ferroelectric and piezoelectric properties of KNN films. Both the remnant polarization P _r and the piezoelectric coefficient d ₃₃ of KNN thick films increase with the film thickness and become saturated after the critical thickness.