Synthesis and Characterization of (Na0.5K0.5)NbO3 (NKN) Thin Films Formed by a Diol-based Sol-gel Process

Lead-free (Na0.5K0.5)NbO3 (NKN) thin films were fabricated by spin coating on Pt/Ti/SiO2/Si substrates by a diol-based sol-gel process. Na-acetate, K-acetate, Nb-pentaethoxide and 1,3 propanediol were used to prepare the NKN precursor solution. Thermal analysis showed two characteristic temperatures of 360 and 600 °C. Based on these temperatures, a heat treatment program with pyrolysis at 360 °C and calcination at 600 °C after every layer was used. To avoid inhomogeneities and secondary phases, an excess of sodium and potassium was necessary. To evaluate the proper excess amount of sodium and potassium secondary ion mass spectrometry (SIMS) lateral element maps and X-ray diffraction (XRD) patterns were recorded. An excess amount of 20% led to homogeneous distribution of the elements and to single phase perovskite NKN films with random crystal orientation. Scanning electron microscopy (SEM) images showed a pore free surface with 100 nm grains. The leakage current measurements showed a current of 1×10−3 A/cm2 at 150 kV/cm.