Preparation of KNbO3 thin films onto alumina substrates by polymeric precursor method

This work presents the development of KNbO3 powders and thin films prepared by the low-cost solution chemical method based on Pechini process. The influence of many synthesis parameters, such as coating solution viscosity, deposition method (dip- or spin-coating), [K / Nb] ratio, heat treatment and effect of multilayers deposition, on the phase formation and microstructure of thin films prepared onto alumina substrates were analyzed. It was verified that using a stoichiometric coating solution, K deficient films are formed. The K amount in the coating solution was increased in order to avoid this deficiency. Single-phased KNbO3 samples were obtained at 550 °C using solutions with [K / Nb]  1.25 and 1.50. These films are continuous, homogeneous and crack-free, and present a thickness about 100 nm per layer. The deposition of multilayers increases the film thickness, as well as it improves its homogeneity and density. Both deposition methods tested, spin- and dip-coating, lead to good results, after deposition parameters optimization. The best results are achieved using coating solution viscosity around 22 × 10− 2 P, dipping and withdrawing speed of 0.16 mm s− 1 for dip-coating and rotation rate around 3000 rpm during 20-40 s for spin-coating.